# Why we need formality in mathematics

The comment thread from my last Cantor crankery post has continued in a way that demonstrates a common issue when dealing with bad math, so I thought it was worth taking the discussion and promoting it to a proper top-level post.

The defender of the Cantor crankery tried to show what he alleged to be the problem with Cantor, by presenting a simple proof:

If we have a unit line, then this line will have an infinite number of points in it. Some of these points will be an irrational distance away from the origin and some will be a rational distance away from the origin.

Premise 1.

To have more irrational points on this line than rational points (plus 1), it is necessary to have at least two irrational points on the line so that there exists no rational point between them.

Premise 2.

It is not possible to have two irrational points on a line so that no rational point exists between them.

Conclusion.

It is not possible to have more irrational points on a line than rational points (plus 1).

This contradicts Cantor’s conclusion, so Cantor must have made a mistake in his reasoning.

(I’ve done a bit of formatting of this to make it look cleaner, but I have not changed any of the content.)

This is not a valid proof. It looks nice on the surface – it intuitively feels right. But it’s not. Why?

Because math isn’t intuition. Math is a formal system. When we’re talking about Cantor’s diagonalization, we’re working in the formal system of set theory. In most modern math, we’re specifically working in the formal system of Zermelo-Fraenkel (ZF) set theory. And that “proof” relies on two premises, which are not correct in ZF set theory. I pointed this out in verbose detail, to which the commenter responded:

I can understand your desire for a proof to be in ZFC, Peano arithmetic and FOPL, it is a good methodology but not the only one, and I am certain that it is not a perfect one. You are not doing yourself any favors if you let any methodology trump understanding. For me it is far more important to understand a proof, than to just know it “works” under some methodology that simply manipulates symbols.

This is the point I really wanted to get to here. It’s a form of complaint that I’ve seen over and over again – not just in the Cantor crankery, but in nearly all of the math posts.

There’s a common belief among crackpots of various sorts that scientists and mathematicians use symbols and formalisms just because we like them, or because we want to obscure things and make simple things seem complicated, so that we’ll look smart.

That’s just not the case. We use formalisms and notation because they are absolutely essential. We can’t do math without the formalisms; we could do it without the notation, but the notation makes things clearer than natural language prose.

The reason for all of that is because we want to be correct.

If we’re working with a definition that contains any vagueness – even the most subtle unintentional kind (or, actually, especially the most subtle unintentional kind!) – then we can easily produce nonsense. There’s a simple “proof” that we’ve discussed before that shows that 0 is equal to 1. It looks correct when you read it. But it contains a subtle error. If we weren’t being careful and formal, that kind of mistake can easily creep in – and once you allow one, single, innocuous looking error into a proof, the entire proof falls apart. The reason for all the formalism and all the notation is to give us a way to unambiguously, precisely state exactly what we mean. The reason that we insist of detailed logical step-by-step proofs is because that’s the only way to make sure that we aren’t introducing errors.

We can’t rely on intuition, because our intuition is frequently not correct. That’s why we use logic. We can’t rely on informal statements, because informal statements lack precision: they can mean many different things, some of which are true, and some of which are not.

In the case of Cantor’s diagonalization, when we’re being carefully precise, we’re not talking about the size of things: we’re talking about the cardinality of sets. That’s an important distinction, because “size” can mean many different things. Cardinality means one, very precise thing.

Similarly, we’re talking about the cardinality of the set of real numbers compared to the cardinality of the set of natural numbers. When I say that, I’m not just hand-waving the real numbers: the real numbers means something very specific: it’s the unique complete totally ordered field $(R, +, *, <)$ up to isomorphism. To understand that, we’re implicitly referencing the formal definition of a field (with all of its sub-definitions) and the formal definitions of the addition, multiplication, and ordering operations.

I’m not just saying that to be pedantic. I’m saying that because we need to know exactly what we’re talking about. It’s very easy to put together an informal definition of the real numbers that’s different from the proper mathematical set of real numbers. For example, you can define a number system consisting of the set of all numbers that can be generated by a finite, non-terminating computer program. Intuitively, it might seem like that’s just another way of describing the real numbers – but it describes a very different set.

Beyond just definitions, we insist on using formal symbolic logic for a similar reason. If we can reduce the argument to symbolic reasoning, then we’ve abstracted away anything that could bias or deceive us. The symbolic logic makes every statement absolutely precise, and every reasoning step pure, precise, and unbiased.

So what’s wrong with the “proof” above? It’s got two premises. Let’s just look at the first one: “To have more irrational points on this line than rational points (plus 1), it is necessary to have at least two irrational points on the line so that there exists no rational point between them.”.

If this statement is true, then Cantor’s proof must be wrong. But is this statement true? The commenter’s argument is that it’s obviously intuitively true.

If we weren’t doing math, that might be OK. But this is math. We can’t just rely on our intuition, because we know that our intuition is often wrong. So we need to ask: can you prove that that’s true?

And how do you prove something like that? Well, you start with the basic rules of your proof system. In a discussion of a set theory proof, that means ZF set theory and first order predicate logic. Then you add in the definitions you need to talk about the objects you’re interested in: so Peano arithmetic, rational numbers, real number theory, and the definition of irrational numbers in real number theory. That gives you a formal system that you can use to talk about the sets of real numbers, rational numbers, and natural numbers.

The problem for our commenter is that you can’t prove that premise using ZF logic, FOPL, and real number theory. It’s not true. It’s based on a faulty understanding of the behavior of infinite sets. It’s taking an assumption that comes from our intuition, which seems reasonable, but which isn’t actually true within the formal system o mathematics.

In particular, it’s trying to say that in set theory, the cardinality of the set of real numbers is equal to the cardinality of the set of natural numbers – but doing so by saying “Ah, Why are you worrying about that set theory nonsense? Sure, it would be nice to prove this statement about set theory using set theory, but you’re just being picky on insisting that.”

Once you really see it in these terms, it’s an absurd statement. It’s equivalent to something as ridiculous as saying that you don’t need to modify verbs by conjugating them when you speak english, because in Chinese, the spoken words don’t change for conjugation.

# Cantor Crankery is Boring

Sometimes, I think that I’m being punished.

I’ve written about Cantor crankery so many times. In fact, it’s one of the largest categories in this blog’s index! I’m pretty sure that I’ve covered pretty much every anti-Cantor argument out there. And yet, not a week goes by when another idiot doesn’t pester me with their “new” refutation of Cantor. The “new” argument is always, without exception, a variation on one of the same old boring ones.

But I haven’t written any Cantor stuff in quite a while, and yet another one landed in my mailbox this morning. So, what the heck. Let’s go down the rabbit-hole once again.

The argument that the cranks hate is called Cantor’s diagonalization. Cantor’s diagonalization as argument that according to the axioms of set theory, the cardinality (size) of the set of real numbers is strictly larger than the cardinality of the set of natural numbers.

The argument is based on the set theoretic definition of cardinality. In set theory, two sets are the same size if and only if there exists a one-to-one mapping between the two sets. If you try to create a mapping between set A and set B, and in every possible mapping, every A is mapped onto a unique B, but there are leftover Bs that no element of A maps to, then the cardinality of B is larger than the cardinality of A.

When you’re talking about finite sets, this is really easy to follow. If I is the set {1, 2, 3}, and B is the set {4, 5, 6, 7}, then it’s pretty obvious that there’s no one to one mapping from A to B: there are more elements in B than there are in A. You can easily show this by enumerating every possible mapping of elements of A onto elements of B, and then showing that in every one, there’s an element of B that isn’t mapped to by an element of A.

With infinite sets, it gets complicated. Intuitively, you’d think that the set of even natural numbers is smaller than the set of all natural numbers: after all, the set of evens is a strict subset of the naturals. But your intuition is wrong: there’s a very easy one to one mapping from the naturals to the evens: {n → 2n }. So the set of even natural numbers is the same size as the set of all natural numbers.

To show that one infinite set has a larger cardinality than another infinite set, you need to do something slightly tricky. You need to show that no matter what mapping you choose between the two sets, some elements of the larger one will be left out.

In the classic Cantor argument, what he does is show you how, given any purported mapping between the natural numbers and the real numbers, to find a real number which is not included in the mapping. So no matter what mapping you choose, Cantor will show you how to find real numbers that aren’t in the mapping. That means that every possible mapping between the naturals and the reals will omit members of the reals – which means that the set of real numbers has a larger cardinality than the set of naturals.

Cantor’s argument has stood since it was first presented in 1891, despite the best efforts of people to refute it. It is an uncomfortable argument. It violates our intuitions in a deep way. Infinity is infinity. There’s nothing bigger than infinity. What does it even mean to be bigger than infinity? That’s a non-sequiter, isn’t it?

What it means to be bigger than infinity is exactly what I described above. It means that if you have a two infinitely large sets of objects, and there’s no possible way to map from one to the other without missing elements, then one is bigger than the other.

There are legitimate ways to dispute Cantor. The simplest one is to reject set theory. The diagonalization is an implication of the basic axioms of set theory. If you reject set theory as a basis, and start from some other foundational axioms, you can construct a version of mathematics where Cantor’s proof doesn’t work. But if you do that, you lose a lot of other things.

You can also argue that “cardinality” is a bad abstraction. That is, that the definition of cardinality as size is meaningless. Again, you lose a lot of other things.

If you accept the axioms of set theory, and you don’t dispute the definition of cardinality, then you’re pretty much stuck.

Ok, background out of the way. Let’s look at today’s crackpot. (I’ve reformatted his text somewhat; he sent this to me as plain-text email, which looks awful in my wordpress display theme, so I’ve rendered it into formatted HTML. Any errors introduced are, of course, my fault, and I’ll correct them if and when they’re pointed out to me.)

We have been told that it is not possible to put the natural numbers into a one to one with the real numbers. Well, this is not true. And the argument, to show this, is so simple that I am absolutely surprised that this argument does not appear on the internet.

We accept that the set of real numbers is unlistable, so to place them into a one to one with the natural numbers we will need to make the natural numbers unlistable as well. We can do this by mirroring them to the real numbers.

Given any real number (between 0 and 1) it is possible to extract a natural number of any length that you want from that real number.

Ex: From π-3 we can extract the natural numbers 1, 14, 141, 1415, 14159 etc…

We can form a set that associates the extracted number with the real number that it was extracted from.

Ex: 1 → 0.14159265…

Then we can take another real number (in any arbitrary order) and extract a natural number from it that is not in our set.

Ex: 1 → 0.14159266… since 1 is already in our set we must extract the next natural number 14.

Since 14 is not in our set we can add the pair 14 → 0.1415926l6… to our set.

We can do the same thing with some other real number 0.14159267… since 1 and 14 is already in our set we will need to extract a 3 digit natural number, 141, and place it in our set. And so on.

So our set would look something like this…

 A) 1 → 0.14159265… B) 14 → 0.14159266… C) 141 → 0.14159267… D) 1410 → 0.141 E) 14101 → 0.141013456789… F) 5 → 0.567895… G) 55 → 0.5567891… H) 555 → 0.555067891… … …

Since the real numbers are infinite in length (some terminate in an infinite string of zero’s) then we can always extract a natural number that is not in the set of pairs since all the natural numbers in the set of pairs are finite in length. Even if we mutate the diagonal of the real numbers, we will get a real number not on the list of real numbers, but we can still find a natural number, that is not on the list as well, to correspond with that real number.

Therefore it is not possible for the set of real numbers to have a larger cardinality than the set of natural numbers!

This is a somewhat clever variation on a standard argument.

Over and over and over again, we see arguments based on finite prefixes of real numbers. The problem with them is that they’re based on finite prefixes. The set of all finite prefixes of the real numbers is that there’s an obvious correspondence between the natural numbers and the finite prefixes – but that still doesn’t mean that there are no real numbers that aren’t in the list.

In this argument, every finite prefix of π corresponds to a natural number. But π itself does not. In fact, every real number that actually requires an infinite number of digits has no corresponding natural number.

This piece of it is, essentially, the same thing as John Gabriel’s crankery.

But there’s a subtler and deeper problem. This “refutation” of Cantor contains the conclusion as an implicit premise. That is, it’s actually using the assumption that there’s a one-to-one mapping between the naturals and the reals to prove the conclusion that there’s a one-to-one mapping between the naturals and the reals.

If you look at his procedure for generating the mapping, it requires an enumeration of the real numbers. You need to take successive reals, and for each one in the sequence, you produce a mapping from a natural number to that real. If you can’t enumerate the real numbers as a list, the procedure doesn’t work.

If you can produce a sequence of the real numbers, then you don’t need this procedure: you’ve already got your mapping. 0 to the first real, 1 to the second real, 2 to the third read, 3 to the fourth real, and so on.

So, once again: sorry Charlie: your argument doesn’t work. There’s no Fields medal for you today.

One final note. Like so many other bits of bad math, this is a classic example of what happens when you try to do math with prose. There’s a reason that mathematicians have developed formal notations, formal language, detailed logical inference, and meticulous citation. It’s because in prose, it’s easy to be sloppy. You can accidentally introduce an implicit premise without meaning to. If you need to carefully state every premise, and cite evidence of its truth, it’s a whole lot harder to make this kind of mistake.

That’s the real problem with this whole argument. It’s built on the fact that the premise “you can enumerate the real numbers” is built in. If you wrote it in careful formal mathematics, you wouldn’t be able to get away with that.

# Bad Math Books and Cantor Cardinality

A bunch of readers sent me a link to a tweet this morning from Professor Jordan Ellenberg:

The tweet links to the following image:

(And yes, this is real. You can see it in context here.)

This is absolutely infuriating.

This is a photo of a problem assignment in a math textbook published by an imprint of McGraw-Hill. And it’s absolutely, unquestionably, trivially wrong. No one who knew anything about math looked at this before it was published.

The basic concept underneath this is fundamental: it’s the cardinality of sets from Cantor’s set theory. It’s an extremely important concept. And it’s a concept that’s at the root of a huge amount of misunderstandings, confusion, and frustration among math students.

Cardinality, and the notion of cardinality relations between infinite sets, are difficult concepts, and they lead to some very un-intuitive results. Infinity isn’t one thing: there are different sizes of infinities. That’s a rough concept to grasp!

Here on this blog, I’ve spent more time dealing with people who believe that it must be wrong – a subject that I call Cantor crackpottery – than with any other bad math topic. This error teaches students something deeply wrong, and it encourages Cantor crackpottery!

Let’s review.

Cantor said that two collections of things are the same size if it’s possible to create a one-to-one mapping between the two. Imagine you’ve got a set of 3 apples and a set of 3 oranges. They’re the same size. We know that because they both have 3 elements; but we can also show it by setting aside pairs of one apple and one orange – you’ll get three pairs.

The same idea applies when you look at infinitely large sets. The set of positive integers and the set of negative integers are the same size. They’re both infinite – but we can show how you can create a one-to-one relation between them: you can take any positive integer $i$, and map it to exactly one negative integer, $0 - i$.

That leads to some unintuitive results. For example, the set of all natural numbers and the set of all even natural numbers are the same size. That seems crazy, because the set of all even natural numbers is a strict subset of the set of natural numbers: how can they be the same size?

But they are. We can map each natural number $i$ to exactly one even natural number $2i$. That’s a perfect one-to-one map between natural numbers and even natural numbers.

Where it gets uncomfortable for a lot of people is when we start thinking about real numbers. The set of real numbers is infinite. Even the set of real numbers between 0 and 1 is infinite! But it’s also larger than the set of natural numbers, which is also infinite. How can that be?

The answer is that Cantor showed that for any possible one-to-one mapping between the natural numbers and the real numbers between 0 and 1, there’s at least one real number that the mapping omitted. No matter how you do it, all of the natural numbers are mapped to one value in the reals, but there’s at least one real number which is not in the mapping!

In Cantor set theory, that means that the size of the set of real numbers between 0 and 1 is strictly larger than the set of all natural numbers. There’s an infinity bigger than infinity.

I think that this is what the math book in question meant to say: that there’s no possible mapping between the natural numbers and the real numbers. But it’s not what they did say: what they said is that there’s no possible map between the integers and the fractions. And that is not true.

Here’s how you generate the mapping between the integers and the rational numbers (fractions) between 0 and 1, written as a pseudo-Python program:

 i = 0
for denom in Natural:
for num in 1 .. denom:
if num is relatively prime with denom:
print("%d => %d/%d" % (i, num, denom))
i += 1


It produces a mapping (0 => 0, 1 => 1, 2 => 1/2, 3 => 1/3, 4 => 2/3, 5 => 1/4, 6 => 3/4, …). It’ll never finish running – but you can easily show that for any possible fraction, there’ll be exactly one integer that maps to it.

That means that the set of all rational numbers between 0 and 1 is the same size as the set of all natural numbers. There’s a similar way of producing a mapping between the set of all fractions and the set of natural numbers – so the set of all fractions is the same size as the set of natural numbers. But both are smaller than the set of all real numbers, because there are many, many real numbers that cannot be written as fractions. (For example, $\pi$. Or the square root of 2. Or $e$. )

This is terrible on multiple levels.

1. It’s a math textbook written and reviewed by people who don’t understand the basic math that they’re writing about.
2. It’s teaching children something incorrect about something that’s already likely to confuse them.
3. It’s teaching something incorrect about a topic that doesn’t need to be covered at all in the textbook. This is an algebra-2 textbook. You don’t need to cover Cantor’s infinite cardinalities in Algebra-2. It’s not wrong to cover it – but it’s not necessary. If the authors didn’t understand cardinality, they could have just left it out.
4. It’s obviously wrong. Plenty of bright students are going to come up with the the mapping between the fractions and the natural numbers. They’re going to come away believing that they’ve disproved Cantor.

I’m sure some people will argue with that last point. My evidence in support of it? I came up with a proof of that in high school. Fortunately, my math teacher was able to explain why it was wrong. (Thanks Mrs. Stevens!) Since I write this blog, people assume I’m a mathematician. I’m not. I’m just an engineer who really loves math. I was a good math student, but far from a great one. I’d guess that every medium-sized high school has at least one math student every year who’s better than I was.

The proof I came up with is absolutely trivial, and I’d expect tons of bright math-geek kids to come up with something like it. Here goes:

1. The set of fractions is a strict subset of the set of ordered pairs of natural numbers.
2. So: if there’s a one-to-one mapping between the set of ordered pairs and the naturals, then there must be a one-to-one mapping between the fractions and the naturals.
3. On a two-d grid, put the natural numbers across, and then down.
4. Zigzag diagonally through the grid, forming pairs of the horizontal position and the vertical position: (0,0), (1, 0), (0, 1), (2, 0), (1, 1), (0, 2), (3, 0), (2, 1), (1, 2), (0, 3).
5. This will produce every possible ordered pair of natural numbers. For each number in the list, produce a mapping between the position in the list, and the pair. So (0, 0) is 0, (2, 0) is 3, etc.

As a proof, it’s sloppy – but it’s correct. And plenty of high school students will come up with something like it. How many of them will walk away believing that they just disproved Cantor?

# Yet Another Cantor Crank: Size vs Cardinality

Over the weekend, a reader sent me links to not one but two new Cantor cranks!

Sadly, one of them is the incoherent sort – the kind of nutjob who strings together words in meaningless ways. Without a certain minimal rationality, there’s nothing I can say. What I try to do on this blog isn’t just make fun of crackpots – it’s explain what they get wrong! If a crackpot strings together words randomly, and no one can make any sense of just what the heck they’re saying, there’s no way to do that.

On the other hand, the second guy is a whole different matter. He’s making a very common mistake, and he’s making it very clearly. So for him, it’s well worth taking a moment and looking at what he gets wrong.

My mantra on this blog has always been: “the worst math is no math”. This is a perfect example.

First, I believe that Cantor derived a false conclusion from the diagonal method.

I believe that the primary error in the theory is not with the assertion that the set of Real Numbers is a “different size” than the set of Integers. The problem lies with the assertion that the set of Rational Numbers is the “same size” as the set of Integers. Our finite notion of size just doesn’t extend to infinite sets. Putting numbers in a list (i.e., creating a one-to-one correspondence between infinite sets) does not show that they are the same “size.”

This becomes clear if we do a two step version of the diagonal method.

Step One: Lets start with the claim: “Putting an infinite set in a list shows that it is the same size as the set of Integers.”

Step Two: Claiming to have a complete list of reals, Cantor uses the diagonal method to create a real number not yet in the list.

Please, think about this two step model. The diagonal method does not show that the rational numbers are denumerable while the real numbers are not. The diagonal method shows that the assertion in step one is false. The assertion in step one is as false for rational numbers as it is for real numbers.

The diagonal method calls into question the cross-section proof used to show that the rational numbers are the same size as the integers.

That might sound like a silly nitpick: it’s just terminology, right?

Wrong. What does size mean? Size is an informal term. It’s got lots of different potential meanings. There’s a reasonable definition of “size” where the set of natural numbers is larger than the set of even natural numbers. It’s a very simple definition: given two sets of objects A and B, the size of B is larger than the size of A if A is a subset of B.

When you say the word “size”, what do you mean? Which definition?

Cantor defined a new way of defining size. It’s not the only valid measure, but it is a valid measure which is widely useful when you’re doing math. The measure he defined is called cardinality. And cardinality, by definition, says that two sets have the same cardinality if and only if it’s possible to create a one-to-one correspondance between the two sets.

When our writer said “Our finite notion of size just doesn’t extend to infinite sets”, he was absolutely correct. The problem is that he’s not doing math! The whole point of Cantor’s work on cardinality was precisely that our finite notion of size doesn’t extend to infinite sets. So he didn’t use our finite notion of size. He defined a new mathematical construct that allows us to meaningfully and consistently talk about the size of infinite sets.

Throughout his website, he builds a complex edifice of reasoning on this basis. It’s fascinating, but it’s ultimately all worthless. He’s trying to do math, only without actually doing math. If you want to try to refute something like Cantor’s diagonalization, you can’t do it with informal reasoning using words. You can only do it using math.

This gets back to a very common error that people make, over and over. Math doesn’t use fancy words and weird notations because mathematicians are trying to confuse non-mathematicians. It’s not done out of spite, or out of some desire to exclude non-mathematicians from the club. It’s about precision.

Cantor didn’t talk about the cardinality of infinite sets because he thought “cardinality” sounded cooler and more impressive than “size”. He did it because “size” is an informal concept that doesn’t work when you scale to infinite sets. He created a new concept because the informal concept doesn’t work. If you’re argument against Cantor is that his concept of cardinality is different from your informal concept of size, you’re completely missing the point.

# Infinite Cantor Crankery

I recently got yet another email from a Cantor crank.

Sadly, it’s not a particularly interesting letter. It contains an argument that I’ve seen more times than I can count. But I realized that I don’t think I’ve ever written about this particular boneheaded nonsense!

I’m going to paraphrase the argument: the original is written in broken english and is hard to follow.

• Cantor’s diagonalization creates a magical number (“Cantor’s number”) based on an infinitely long table.
• Each digit of Cantor’s number is taken from one row of the table: the Nth digit is produced by the Nth row of the table.
• This means that the Nth digit only exists after processing N rows of the table.
• Suppose it takes time t to get the value of a digit from a row of the table.
• Therefore, for any natural number N, it takes N*t time to get the first N digits of Cantor’s number.
• Any finite prefix of Cantor’s number is a rational number, which is clearly in the table.
• The full Cantor’s number doesn’t exist until an infinite number of steps has been completed, at time &infinity;*t.
• Therefore Cantor’s number never exists. Only finite prefixes of it exist, and they are all rational numbers.

The problem with this is quite simple: Cantor’s proof doesn’t create a number; it identifies a number.

It might take an infinite amount of time to figure out which number we’re talking about – but that doesn’t matter. The number, like all numbers, exists, independent of
our ability to compute it. Once you accept the rules of real numbers as a mathematical framework, then all of the numbers, every possible one, whether we can identify it, or describe it, or write it down – they all exist. What a mechanism like Cantor’s diagonalization does is just give us a way of identifying a particular number that we’re interested in. But that number exists, whether we describe it or identify it.

The easiest way to show the problem here is to think of other irrational numbers. No irrational number can ever be written down completely. We know that there’s got to be some number which, multiplied by itself, equals 2. But we can’t actually write down all of the digits of that number. We can write down progressively better approximations, but we’ll never actually write the square root of two. By the argument above against Cantor’s number, we can show that the square root of two doesn’t exist. If we need to create the number by writing down all af its digits,s then the square root of two will never get created! Nor will any other irrational number. If you insist on writing numbers down in decimal form, then neither will many fractions. But in math, we don’t create numbers: we describe numbers that already exist.

But we could weasel around that, and create an alternative formulation of mathematics in which all numbers must be writeable in some finite form. We wouldn’t need to say that we can create numbers, but we could constrain our definitions to get rid of the nasty numbers that make things confusing. We could make a reasonable argument that those problematic real numbers don’t really exist – that they’re an artifact of a flaw in our logical definition of real numbers. (In fact, some mathematicians like Greg Chaitin have actually made that argument semi-seriously.)

By doing that, irrational numbers could be defined out of existence, because they
can’t be written down. In essence, that’s what my correspondant is proposing: that the definition of real numbers is broken, and that the problem with Cantor’s proof is that it’s based on that faulty definition. (I don’t think that he’d agree that that’s what he’s arguing – but either numbers exist that can’t be written in a finite amount of time, or they don’t. If they do, then his argument is worthless.)

You certainly can argue that the only numbers that should exist are numbers that can be written down. If you do that, there are two main paths. There’s the theory of computable numbers (which allows you to keep π and the square roots), and there’s the theory of rational numbers (which discards everything that can’t be written as a finite fraction). There are interesting theories that build on either of those two approaches. In both, Cantor’s argument doesn’t apply, because in both, you’ve restricted the set of numbers to be a countable set.

But that doesn’t say anything about the theory of real numbers, which is what Cantor’s proof is talking about. In the real numbers, numbers that can’t be written down in any form do exist. Numbers like the number produced by Cantor’s diagonalization definitely do. The infinite time argument is a load of rubbish because it’s based on the faulty concept that Cantor’s number doesn’t exist until we create it.

The interesting thing about this argument to be, is its selectivity. To my correspondant, the existence of an infinitely long table isn’t a problem. He doesn’t think that there’s anything wrong with the idea of an infinite process creating an infinite table containing a mapping between the natural numbers and the real numbers. He just has a problem with the infinite process of traversing that table. Which is really pretty silly when you think about it.

# Speed-Crankery

A fun game to play with cranks is: how long does it take for the crank to contradict themselves?

When you’re looking at a good example of crankery, it’s full of errors. But for this game, it’s not enough to just find an error. What we want is for them to say something so wrong that one sentence just totally tears them down and demonstrates that what they’re doing makes no sense.

“The color of a clear sky is green” is, most of the time, wrong. If a crank makes some kind of argument based on the alleged fact that the color of a clear daytime sky is green, the argument is wrong. But as a statement, it’s not nonsensical. It’ just wrong.

On th other hand, “The color of a clear sky is steak frite with bernaise sauce and a nice side of roasted asparagus”, well… it’s not even wrong. It’s just nonsense.

Today’s crank is a great example of this. If, that is, it’s legit. I’m not sure that this guy is serious. I think this might be someone playing games, pretending to be a crank. But even if it is, it’s still fun.

About a week ago, I got en mail titled “I am a Cantor crank” from a guy named Chris Cuellar. The contents were:

…AND I CHALLENGE YOU TO A DUEL!! En garde!

Haha, ok, not exactly. But you really seem to be interested in this stuff. And so am I. But I think I’ve nailed Cantor for good this time. Not only have I come up with algorithms to count some of these “uncountable” things, but I have also addressed the proofs directly. The diagonalization argument ends up failing spectacularly, and I believe I have a good explanation for why the whole thing ends up being invalid in the first place.

And then I also get to the power set of natural numbers… I really hope my arguments can be followed. The thing I have to emphasize is that I am working on a different system that does NOT roll up cardinality and countability into one thing! As it will turn out, rational numbers are bigger than integers, integers are bigger than natural numbers… but they are ALL countable, nonetheless!

Anyway, I had started a little blog of my own a while ago on these subjects. The first post is here:
http://laymanmath.blogspot.com/2012/09/the-purpose-and-my-introduction.html

Have fun… BWAHAHAHA

So. We’ve got one paragraph of intro. And then everything crashes and burns in an instant.

“Rational numbers are bigger than integers, integers are bigger than natural numbers, but they are all countable”. This is self-evident rubbish. The definition of “countable” say that an infinite set I is countable if, and only if, you can create a one-to-one mapping between the members of I and the natural numbers. The definition of cardinality says that if you can create a one-to-one mapping between two sets, the sets are the same size.

When Mr. Cuellar says that the set of rational numbers is bigger that the set of natural numbers, but that they are still countable… he’s saying that there is not a one-to-one mapping between the two sets, but that there is a one-to-one mapping between the two sets.

Look – you don’t get to redefine terms, and then pretend that your redefined terms mean the same thing as the original terms.

If you claim to be refuting Cantor’s proof that the cardinality of the real numbers is bigger than the cardinality of the natural numbers, then you have to use Cantor’s definition of cardinality.

You can change the definition of the size of a set – or, more precisely, you can propose an alternative metric for how to compare the sizes of sets. But any conclusions that you draw about your new metric are conclusions about your new metric – they’re not conclusions about Cantor’s cardinality. You can define a new notion of set size in which all infinite sets are the same size. It’s entirely possible to do that, and to do that in a consistent way. But it will say nothing about Cantor’s cardinality. Cantor’s proof will still work.

What my correspondant is doing is, basically, what I did above in saying that the color of the sky is steak frites. I’m using terms in a completely inconsistent meaningless way. Steak frites with bernaise sauce isn’t a color. And what Mr. Cuellar does is similar: he’s using the word “cardinality”, but whatever he means by it, it’s not what Cantor meant, and it’s not what Cantor’s proof meant. You can draw whatever conclusions you want from your new definition, but it has no bearing on whether or not Cantor is correct. I don’t even need to visit his site: he’s demonstrated, in record time, that he has no idea what he’s doing.

# Genius Continuum Crackpottery

This post was revised on June 25, 2014. Mr. Wince has been threatening to sue me for libel. I don’t think that that’s right, but one thing that he’s complained about is correct. I called him a high school dropout. In his article, Wince refers to “when he dropped out of high school”, but in the same sentence, he goes on to say that he dropped out to attend community college. Calling him a dropout is a cheap shot, which I shouldn’t have included, and for that, I apologize. I’ve removed the line from the post. I still think that his math is laughably wrong, but I shouldn’t have called him a dropout.

There’s a lot of mathematical crackpottery out there. Most of it is just pointless and dull. People making the same stupid mistakes over and over again, like the endless repetitions of the same-old supposed refutations of Cantor’s diagonalization.

After you eliminate that, you get reams of insanity – stuff which
is simply so incoherent that it doesn’t make any sense. This kind of thing is usually word salad – words strung together in ways that don’t make sense.

After you eliminate that, sometimes, if you’re really lucky, you’ll come accross something truly special. Crackpottery as utter genius. Not genius in a good way, like they’re an outsider genius who discovered something amazing, but genius in the worst possible way, where someone has created something so bizarre, so overwrought, so utterly ridiculous that it’s a masterpiece of insane, delusional foolishness.

Today, we have an example of that: Existics!. This is a body of work by a guy named Gavin Wince with truly immense delusions of grandeur. Pomposity on a truly epic scale!

I’ll walk you through just a tiny sample of Mr. Wince’s genius. You can go look at his site to get more, and develop a true appreciation for this. He doesn’t limit himself to mere mathematics: math, physics, biology, cosmology – you name it, Mr. Wince has mastered it and written about it!

The best of his mathematical crackpottery is something called C3: the Canonized Cardinal Continuum. Mr. Wince has created an algebraic solution to the continuum hypothesis, and along the way, has revolutionized number theory, algebra, calculus, real analysis, and god only knows what else!

Since Mr. Wince believes that he has solved the continuum hypothesis. Let me remind you of what that is:

1. If you use Cantor’s set theory to explore numbers, you get to the uncomfortable result that there are different sizes of infinity.
2. The smallest infinite cardinal number is called ℵ0,
and it’s the size of the set of natural numbers.
3. There are cardinal numbers larger than ℵ0. The first
one larger than ℵ0 is ℵ1.
4. We know that the set of real numbers is the size of the powerset
of the natural numbers – 20 – is larger than the set of the naturals.
5. The question that the continuum hypothesis tries to answer is: is the size
of the set of real numbers equal to ℵ1? That is, is there
a cardinal number between ℵ0 and |20|?

The continuum hypothesis was “solved” in 1963. In 1940, Gödel showed that you couldn’t disprove the continuum hypothesis using ZFC. In 1963,
another mathematician named Paul Cohen, showed that it couldn’t be proven using ZFC. So – a hypothesis which is about set theory can be neither proven nor disproven using set theory. It’s independent of the axioms of set theory. You can choose to take the continuum hypothesis as an axiom, or you can choose to take the negation of the continuum hypothesis as an axiom: either choice is consistent and valid!

It’s not a happy solution. But it’s solved in the sense that we’ve got a solid proof that you can’t prove it’s true, and another solid proof that you can’t prove it’s false. That means that given ZFC set theory as a basis, there is no proof either way that doesn’t set it as an axiom.

But… Mr. Wince knows better.

The set of errors that Wince makes is really astonishing. This is really seriously epic crackpottery.

He makes it through one page without saying anything egregious. But then he makes up for it on page 2, by making multiple errors.

First, he pulls an Escultura:

x1 = 1/21 = 1/2 = 0.5
x2 = 1/21 + 1/22 = 1/2 + 1/4 = 0.75
x3 = 1/21 + 1/22 + 1/23 = 1/2 + 1/4 + 1/8 = 0.875

At the end or limit of the infinite sequence, the final term of the sequence is 1.0

In this example we can see that as the number of finite sums of the sequence approaches the limit infinity, the last term of the sequence equals one.
xn = 1.0
If we are going to assume that the last term of the sequence equals one, it can be deduced that, prior to the last term in the sequence, some finite sum in the series occurs where:
xn-1 = 0.999…
xn-1 = 1/21 + 1/22 + 1/23 + 1/24 + … + 1/2n-1 = 0.999…
Therefore, at the limit, the last term of the series of the last term of the sequence would be the term, which, when added to the sum 0.999… equals 1.0.

There is no such thing as the last term of an infinite sequence. Even if there were, the number 0.999…. is exactly the same as 1. It’s a notational artifact, not a distinct number.

But this is the least of his errors. For example, the first paragraph on the next page:

The set of all countable numbers, or natural numbers, is a subset of the continuum. Since the set of all natural numbers is a subset of the continuum, it is reasonable to assume that the set of all natural numbers is less in degree of infinity than the set containing the continuum.

We didn’t need to go through the difficult of Cantor’s diagonalization! We could have just blindly asserted that it’s obvious!

or actually… The fact that there are multiple degrees of infinity is anything but obvious. I don’t know anyone who wasn’t surprised the first time they saw Cantor’s proof. It’s a really strange idea that there’s something bigger than infinity.

Moving on… the real heart of his stuff is built around some extremely strange notions about infinite and infinitessimal values.

Before we even look at what he says, there’s an important error here
which is worth mentioning. What Mr. Wince is trying to do is talk about the
continuum hypothesis. The continuum hypothesis is a question about the cardinality of the set of real numbers and the set of natural numbers.
Neither infinites nor infinitessimals are part of either set.

Infinite values come into play in Cantor’s work: the cardinality of the natural numbers and the cardinality of the reals are clearly infinite cardinal numbers. But ℵ0, the smallest infinite cardinal, is not a member of either set.

Infinitessimals are fascinating. You can reconstruct differential and integral calculus without using limits by building in terms of infinitessimals. There’s some great stuff in surreal numbers playing with infinitessimals. But infinitessimals are not real numbers. You can’t reason about them as if they were members of the set of real numbers, because they aren’t.

Many of his mistakes are based on this idea.

For example, he’s got a very strange idea that infinites and infinitessimals don’t have fixed values, but that their values cover a range. The way that he gets to that idea is by asserting the existence
of infinity as a specific, numeric value, and then using it in algebraic manipulations, like taking the “infinityth root” of a real number.

For example, on his way to “proving” that infinitessimals have this range property that he calls “perambulation”, he defines a value that he calls κ:

$sqrt[infty]{infty} = 1 + kappa$

In terms of the theory of numbers, this is nonsense. There is no such thing as an infinityth root. You can define an Nth root, where N is a real number, just like you can define an Nth power – exponents and roots are mirror images of the same concept. But roots and exponents aren’t defined for infinity, because infinity isn’t a number. There is no infinityth root.

You could, if you really wanted to, come up with a definition of exponents that that allowed you to define an infinityth root. But it wouldn’t be very interesting. If you followed the usual pattern for these things, it would be a limit: $sqrt[infty]{x} lim_{nrightarrowinfty} sqrt[n]{x}$. That’s clearly 1. Not 1 plus something: just exactly 1.

But Mr. Cringe doesn’t let himself be limited by silly notions of consistency. No, he defines things his own way, and runs with it. As a result, he gets a notion that he calls perambulation. How?

Take the definition of κ:

$sqrt[infty]{infty} = 1 + kappa$

Now, you can, obviously, raise both sides to the power of infinity:

$infty = (1 + kappa)^{infty}$

Now, you can substitute ℵ0 for $infty$. (Why? Don’t ask why. You just can.) Then you can factor it. His factoring makes no rational sense, so I won’t even try to explain it. But he concludes that:

• Factored and simplified one way, you end up with (κ+1) = 1 + x, where x is some infinitessimal number larger than κ. (Why? Why the heck not?)
• Factored and simplified another way, you end up with (κ+1) = ℵ
• If you take the mean of of all of the possible factorings and reductions, you get a third result, that (κ+1) = 2.

He goes on, and on, and on like this. From perambulation to perambulating reciprocals, to subambulation, to ambulation. Then un-ordinals, un-sets… this is really an absolute masterwork of utter insane crackpottery.

# For every natural number N, there's a Cantor Crank C(n)

More crankery? of course! What kind? What else? Cantor crankery!

It’s amazing that so many people are so obsessed with Cantor. Cantor just gets under peoples’ skin, because it feels wrong. How can there be more than one infinity? How can it possibly make sense?

As usual in math, it all comes down to the axioms. In most math, we’re working from a form of set theory – and the result of the axioms of set theory are quite clear: the way that we define numbers, the way that we define sizes, this is the way it is.

Today’s crackpot doesn’t understand this. But interestingly, the focus of his problem with Cantor isn’t the diagonalization. He thinks Cantor went wrong way before that: Cantor showed that the set of even natural numbers and the set of all natural numbers are the same size!

Unfortunately, his original piece is written in Portuguese, and I don’t speak Portuguese, so I’m going from a translation, here.

The Brazilian philosopher Olavo de Carvalho has written a philosophical “refutation” of Cantor’s theorem in his book “O Jardim das Aflições” (“The Garden of Afflictions”). Since the book has only been published in Portuguese, I’m translating the main points here. The enunciation of his thesis is:

Georg Cantor believed to have been able to refute Euclid’s fifth common notion (that the whole is greater than its parts). To achieve this, he uses the argument that the set of even numbers can be arranged in biunivocal correspondence with the set of integers, so that both sets would have the same number of elements and, thus, the part would be equal to the whole.

And his main arguments are:

It is true that if we represent the integers each by a different sign (or figure), we will have a (infinite) set of signs; and if, in that set, we wish to highlight with special signs, the numbers that represent evens, then we will have a “second” set that will be part of the first; and, being infinite, both sets will have the same number of elements, confirming Cantor’s argument. But he is confusing numbers with their mere signs, making an unjustifiable abstraction of mathematical properties that define and differentiate the numbers from each other.

The series of even numbers is composed of evens only because it is counted in twos, i.e., skipping one unit every two numbers; if that series were not counted this way, the numbers would not be considered even. It is hopeless here to appeal to the artifice of saying that Cantor is just referring to the “set” and not to the “ordered series”; for the set of even numbers would not be comprised of evens if its elements could not be ordered in twos in an increasing series that progresses by increments of 2, never of 1; and no number would be considered even if it could be freely swapped in the series of integeres.

He makes two arguments, but they both ultimately come down to: “Cantor contradicts Euclid, and his argument just can’t possibly make sense, so it must be wrong”.

The problem here is: Euclid, in “The Elements”, wrote severaldifferent collections of axioms as a part of his axioms. One of them was the following five rules:

1. Things which are equal to the same thing are also equal to one another.
2. If equals be added to equals, the wholes are equal.
3. If equals be subtracted from equals, the remainders are equal.
4. Things which coincide with one another are equal to one another.
5. The whole is greater that the part.

The problem that our subject has is that Euclid’s axiom isn’t an axiom of mathematics. Euclid proposed it, but it doesn’t work in number theory as we formulate it. When we do math, the axioms that we start with do not include this axiom of Euclid.

In fact, Euclid’s axioms aren’t what modern math considers axioms at all. These aren’t really primitive ground statements. Most of them are statements that are provable from the actual axioms of math. For example, the second and third axioms are provable using the axioms of Peano arithmetic. The fourth one doesn’t appear to be a statement about numbers at all; it’s a statement about geometry. And in modern terms, the fifth one is either a statement about geometry, or a statement about measure theory.

The first argument is based on some strange notion of signs distinct from numbers. I can’t help but wonder if this is an error in translation, because the argument is so ridiculously shallow. Basically, it concedes that Cantor is right if we’re considering the representations of numbers, but then goes on to draw a distinction between representations (“signs”) and the numbers themselves, and argues that for the numbers, the argument doesn’t work. That’s the beginning of an interesting argument: numbers and the representations of numbers are different things. It’s definitely possible to make profound mistakes by confusing the two. You can prove things about representations of numbers that aren’t true about the numbers themselves. Only he doesn’t actually bother to make an argument beyond simply asserting that Cantor’s proof only works for the representations.

That’s particularly silly because Cantor’s proof that the even naturals and the naturals have the same cardinality doesn’t talk about representation at all. It shows that there’s a 1 to 1 mapping between the even naturals and the naturals. Period. No “signs”, no representations.

The second argument is, if anything, even worse. It’s almost the rhetorical equivalent of sticking his fingers in his ears and shouting “la la la la la”. Basically – he says that when you’re producing the set of even naturals, you’re skipping things. And if you’re skipping things, those things can’t possible be in the set that doesn’t include the skipped things. And if there are things that got skipped and left out, well that means that it’s ridiculous to say that the set that included the left out stuff is the same size as the set that omitted the left out stuff, because, well, stuff got left out!!!.

Here’s the point. Math isn’t about intuition. The properties of infinitely large sets don’t make intuitive sense. That doesn’t mean that they’re wrong. Things in math are about formal reasoning: starting with a valid inference system and a set of axioms, and then using the inference to reason. If we look at set theory, we use the axioms of ZFC. And using the axioms of ZFC, we define the size (or, technically, the cardinality) of sets. Using that definition, two sets have the same cardinality if and only if there is a one-to-one mapping between the elements of the two sets. If there is, then they’re the same size. Period. End of discussion. That’s what the math says.

Cantor showed, quite simply, that there is such a mapping:

${ (i rightarrow itimes 2) | i in N }$

There it is. It exists. It’s simple. It works, by the axioms of Peano arithmetic and the axiom of comprehension from ZFC. It doesn’t matter whether it fits your notion of “the whole is greater than the part”. The entire proof is that set comprehension. It exists. Therefore the two sets have the same size.

# There's always more Cantor crackpottery!

I’m not the only one who gets mail from crackpots!

A kind reader forwarded me yet another bit of Cantor crackpottery. It never ceases to amaze me how many people virulently object to Cantor, and how many of them just spew out the same, exact, rubbish, somehow thinking that they’re different than all the others who made the same argument.

This one is yet another in the representation scheme. That is, it’s an argument that I can write out all of the real numbers whose decimal forms have one digit after the decimal point; then all of the reals with two digits; then all of them with 3 digits; etc. This will produce an enumeration, therefore, there’s a one-to-one mapping from the naturals to the reals. Presto, Cantor goes out the window.

Or not.

As usual, the crank starts off with a bit of pomposity:

Dear Colleague,

My mathematic researshes lead me to resolve the continuum theory of Cantor, subject of controversy since a long time.

This mail is made to inform the mathematical community from this work, and share the conclusions.

You will find in attachment extracts from my book “Théorie critique fondamentale des ensembles de Cantor”,

Inviting you to contact me,

Francis Collot,
Member of the American mathematical society
Membre de la société mathématique de France
Member of the Bulletin of symbolic logic
Director of éditions européennes

As a quick aside, I love how he signs he email “Member of the AMS”, as if that were something meaningful. The AMS is a great organization – but anyone can be a member. All you need to do is fill out a form, and write them a check. It’s not something that anyone sane or reasonable brags about, because it doesn’t mean anything.

Anyway, let’s move on. Here’s the entirety of his proof. I’ve reproduced the formatting as well as I could; the original document sent to me was a PDF, so the tables don’t cut-and-paste.

The well-order on the set of real numbers result from this remark that it is possible to build, after the comma, a set where each subset has the same number of ordered elements (as is ordered the subset 2 : 10 …13 … 99).

Each successive integer is able to be followed after the comma (in french the real numbers have one comma after the integer) by an increasing number of figures.

 0,0 0,10 0,100 0,1 0,11 0,101 0,2 0,12 0,102 … … … 0,9 0,99 0,999

It is the same thing for each successive interger before the comma.

1 2 3

So it is the 2 infinite of real number.

For this we use the binary notation.

But Cantor and his disciples never obtained this simple result.

After that, the theory displays that the infinity is the asymptote of the two branches of the hyperbole thanks to an introduction of trigonometry notions.

The successive numbers which are on cotg (as 1/2, 1/3, 1/4, 1/5) never attain 0 because it would be necessary to write instead (1/2, 1/3, 1/4, 1/4 ).

The 0 of the cotg is also the origin of the asymptote, that is to say infinite.

The beginning is, pretty much, a typical example of the representational crankery. It’s roughly a restatement of, for example, John Gabriel and his decimal trees. The problem with it is simple: this kind of enumeration will enumerate all of the real numbers with finite length representations. Which means that the total set of values enumerated by this won’t even include all of the rational numbers, much less all of the real numbers.

(As an interesting aside: you can see a beautiful example of what Mr. Collot missed by looking at Conway’s introduction to the surreal numbers, On Numbers and Games, which I wrote about here. He specifically deals with this problem in terms of “birthdays” and the requirement to include numbers who have an infinite birthday, and thus an infinite representation in the surreal numbers.)

After the enumeration stuff, he really goes off the rails. I have no idea what that asymptote nonsense is supposed to mean. I think part of the problem is that mr. Collot isn’t very good at english, but the larger part of it is that he’s an incoherent crackpot.

# Yet Another Cantor Crank

I get a fair bit of mail from crackpots. The category that I find most annoying is the Cantor cranks. Over and over and over again, these losers send me their “proofs”.

What Cantor did was remarkably elegant. He showed that given anything that is claimed to be a one-to-one mapping between the set of integers and the set of real numbers (also sometimes described as an enumeration of the real numbers – the two terms are functionally equivalent), then here’s a simple procedure which will produce a real number that isn’t in included in that mapping – which shows that the mapping isn’t one-to-one.

The problem with the run-of-the-mill Cantor crank is that they never even try to actually address Cantor’s proof. They just say “look, here’s a mapping that works!”

So the entire disproof of their “refutation” of Cantor’s proof is… Cantor’s proof. They completely ignore the thing that they’re claiming to disprove.

I got another one of these this morning. It’s particularly annoying because he makes the same mistake as just about every other Cantor crank – but he also specifically points to one of my old posts where I rant about people who make exactly the same mistake as him.

To add insult to injury, the twit insisted on sending me PDF – and not just a PDF, but a bitmapped PDF – meaning that I can’t even copy text out of it. So I can’t give you a link; I’m not going to waste Scientopia’s bandwidth by putting it here for download; and I’m not going to re-type his complete text. But I’ll explain, in my own compact form, what he did.

It’s an old trick; for example, it’s ultimately not that different from what John Gabriel did. The only real novelty is that he does it in binary – which isn’t much of a novelty. This author calls it the “mirror method”. The idea is, in one column, write a list of the integers greater than 0. In the opposite column, write the mirror of that number, with the decimal (or, technically, binary) point in front of it:

Integer Real
0 0.0
1 0.1
10 0.01
11 0.11
100 0.001
101 0.101
110 0.011
111 0.111
1000 0.0001

Extend that out to infinity, and, according to the author, the second column it’s a sequence of every possible real number, and the table is a complete mapping.

The problem is, it doesn’t work, for a remarkably simple reason.

There is no such thing as an integer whose representation requires an infinite number of digits. For every possible integer, its representation in binary has a fixed number of bits: for any integer N, it’s representation is no longer that $lceil log_2(n) rceil$. That’s always a finite integer.

But… we know that the set of real numbers includes numbers whose representation is infinitely long. so this enumeration won’t include them. Where does the square root of two fall in this list? It doesn’t: it can’t be written as a finite string in binary. Where is π? It’s nowhere; there’s no finite representation of π in binary.

The author claims that the novel property of his method is:

Cantor proved the impossibility of both our enumerations as follows: for any given enumeration like ours Cantor proposed his famous diagonal method to build the contra-sample, i.e., an element which is quasi omitted in this enumeration. Before now, everyone agreed that this element was really omitted as he couldn’t tell the ordinal number of this element in the give enumeration: now he can. So Cantor’s contra-sample doesn’t work.

This is, to put it mildly, bullshit.

First of all – he pretends that he’s actually addressing Cantor’s proof – only he really isn’t. Remember – what Cantor’s proof did was show you that, given any purported enumeration of the real numbers, that you could construct a real number that isn’t in that enumeration. So what our intrepid author did was say “Yeah, so, if you do Cantor’s procedure, and produce a number which isn’t in my enumeration, then I’ll tell you where that number actually occurred in our mapping. So Cantor is wrong.”

But that doesn’t actually address Cantor. Cantor’s construction specifically shows that the number it constructs can’t be in the enumeration – because the procedure specifically guarantees that it differs from every number in the enumeration in at least one digit. So it can’t be in the enumeration. If you can’t show a logical problem with Cantor’s construction, then any argument like the authors is, simply, a priori rubbish. It’s just handwaving.

But as I mentioned earlier, there’s an even deeper problem. Cantor’s method produces a number which has an infinitely long representation. So the earlier problem – that all integers have a finite representation – means that you don’t even need to resort to anything as complicated as Cantor to defeat this. If your enumeration doesn’t include any infinitely long fractional values, then it’s absolutely trivial to produce values that aren’t included: 1/3, 1/7, 1/9.

In short: stupid, dull, pointless; absolutely typical Cantor crankery.