Questions tagged [set-theory]

For questions about the mathematical branch that is based on the study of sets, i.e. collections of objects.

Filter by
Sorted by
Tagged with
0 votes
0 answers
330 views

Has Cantor's irregular enumeration of rationals ever been discussed?

Enumeration of all positive fractions recently has gained renewed interest (see the list below). By translation invariance we can be sure that in all intervals (n, n+1] of the real axis, there are the ...
1 vote
1 answer
108 views

What problem was Borel trying to solve?

I may be mistaken but I understood that Borel developed his sigma algebra before Lebesgue developed his measure. If correct, then Borel can't have been trying to find a collection of sets in $\mathbb{...
5 votes
4 answers
1k views

Kronecker vs Cantor — who won?

Now set theory is taught even to kids and it is the foundation of mathematics. Can we say that Cantor won?
13 votes
0 answers
370 views

Did Kronecker say that set theory is not mathematics?

I have frequently come across Kronecker's statement about set theory: I don't know what predominates in Cantor's theory - philosophy or theology, but I am sure that there is no mathematics there. It ...
5 votes
1 answer
311 views

Why was Kronecker dissatisfied with Cantor's submitted paper?

It is said here that In 1874 Cantor published an article in Crelle's Journal which marks the birth of set theory. A follow-up paper was submitted by Cantor to Crelle's Journal in 1878 but already set ...
4 votes
1 answer
124 views

Did Cantor coin the terms countable and uncountable? If not, who did?

I just assumed that he did since we owe the proof that $\mathbb{R}$ is uncountable to him, but a search of my favorite source for answering such questions -- https://mathshistory.st-andrews.ac.uk/...
1 vote
0 answers
71 views

The definition of 'countable' and 'finite' set

I have an equivalent definition of finite and countable sets that seems 'less' based on set theory than the usual definitions. I am wondering if anyone has encountered these definitions anywhere, esp....
1 vote
0 answers
85 views

where does trace $\sigma$-algebra come from

I came across the term trace $\sigma$-algebra in the context of conditional probability. Does anyone know where it comes from? i found a reference to trace of a matrix here: https://mathshistory.st-...
5 votes
1 answer
275 views

Definition of ordinal multiplication

The ordinal multiplication $\cdot$ can be defined recursively via ordinal addition $+$ for any ordinal $\alpha$ as follows: $\alpha\cdot 0=0$. $\alpha\cdot (\beta+1)=\alpha\cdot \beta+\alpha$ for any ...
0 votes
1 answer
132 views

When did Zermelo and Fraenkel publish their axioms?

I have googled the heck out of this but cannot find a reference to the year Z&F published their axioms. I'd expected to see an article reference but none that I could find.
17 votes
1 answer
2k views

How did mathematicians notate the empty set before $\varnothing$?

Recently, I learned that $\emptyset$ or $\varnothing$ is a relatively new notation for the empty set and was created in 1939. I know $\{\}$ is also used along with $\{\cdot\}$ to denote empty sets. ...
4 votes
0 answers
122 views

What role has Whitehead's Conjecture played in the thinking on the plurality of set theories?

I am curious about the history of the Whitehead's Conjecture, as this was the first natural mathematical statement, in the sense that mathematicians were actually interested in the answer, that was ...
4 votes
2 answers
451 views

When did set theory throw off theology?

"The general set theory [...] definitely belongs to metaphysics. You can easily convince yourself when examining the categories of cardinal numbers and the order type, these basic notions of set ...
11 votes
2 answers
678 views

How much did scholasticism contribute to logic and mathematics?

I occasionally encounter mentions suggesting that late middle ages weren't as barren intellectually as commonly believed. For example, Occam and Scotus are credited with developing modal and ...
9 votes
1 answer
646 views

Origin of Q for the set of rational numbers?

It seems many sources$^1$ attribute the use of the letter "Q" to represent the rationals to the N. Bourbaki group (in the 1930's); however, the Wikipedia entry on rational numbers claims ...
8 votes
1 answer
222 views

Origin / first use of $\mathbb{Z}$ (blackboard bold Z)?

I'm aware that the choice of "Z" comes from German zahlen (for "numbers"); however, I was curious to know when the dedicated font, which I believe is called "blackboard bold&...
2 votes
0 answers
100 views

Where can I find the actual first order formulation of ZFC Axioms?

I'm currently writing my thesis about ZFC origins, and I need a source from where to know who gives the actual first order formulation of ZFC. I got to the point where Bernays writes about it and ...
7 votes
2 answers
2k views

Did Poincaré say that set theory is a disease?

This question has been discussed on several sites including MathOverflow but with not definite result. Presumely HSE is best suited. Jeremy Gray denies that Poincare said, "Later generations will ...
8 votes
1 answer
295 views

What were the not-so-convincing reasons for using the word "power" for power sets?

A footnote of Enderton's Elements of Set Theory (1977, page 4) for the definition of power set states that the reasons for using the word "power" in this context are not very convincing, but the ...
3 votes
2 answers
432 views

Who discovered the difference between the infinities?

As we know, there is a difference between the (infinite) size (or cardinality) of the integer numbers and the size of the reals ($\aleph_0$ and $\mathfrak c=2^{\aleph_0}$). Who discovered it first?
11 votes
1 answer
967 views

How many important logicians did NOT receive doctoral degrees?

I can think of three. Saul Kripke quite famously could only be begrudged to finish his undergraduate degree at Harvard before being hired as a full professor. Donald Martin (the set theorist of Martin'...
11 votes
4 answers
2k views

How was Fourier analysis important to the development of set theory?

I recently read the following quote (unfortunately, I copied it down without attribution): You may be surprised to know that Fourier analysis played a role in the early development of set theory. In ...
13 votes
3 answers
568 views

Why did Cantor (and others) use $\mathfrak{c}$ for the continuum?

Kontinuum is German for continuum, but Cantor used $\mathfrak{c}$. Revision. J.W.Perry questions whether or not Cantor ever in fact used the symbol $\mathfrak{c}$. I must admit I just assumed that he ...
3 votes
1 answer
406 views

How did ZFC become the standard foundations of mathematics?

I would like to hear about the historical and technical reasons for why Zermelo-Fraenkel set theory with the axiom of Choice became the dominant standard for the foundations of mathematics. The system ...
15 votes
1 answer
621 views

Did du Bois-Reymond invent the diagonal argument before Cantor?

The Wiki article on Cantor's diagonal argument mentions that the first use of a diagonal argument was in the work of Paul du Bois-Reymond in 1875. This would be one year after Cantor's first proof of ...
4 votes
3 answers
630 views

What brought about the need for real analysis and formal logic in recent years?

I can't seem to find a clear, definitive, non-circular answer on this. For centuries and centuries, we've been doing mathematics in one form or another, be it geometry and pictures, or inventing ...
2 votes
1 answer
258 views

Cantor's fortune

Wiki says that his transfinite numbers met opposition: Henri Poincaré referred to his ideas as a "grave disease" infecting the discipline of mathematics, and Leopold Kronecker's public ...
3 votes
0 answers
150 views

Translations of "Sur le théorème de Zorn"?

Are there any translations of the following into English, German, or Russian? Nicolas Bourbaki, Sur le théorème de Zorn, Archiv der Mathematik, Volume 2, pages 434–437, November 1949. Any help is ...
4 votes
1 answer
332 views

Was Hilbert ambivalent about set theory?

There is the well-known quote of Hilbert: "No one shall drive us from the paradise which Cantor has created for us." [D. Hilbert: "Über das Unendliche", Mathematische Annalen 95 (...
9 votes
1 answer
1k views

What are the origins of Galileo's paradox?

Galileo's paradox is the observation that the natural numbers can be put into one to one correspondence with the square numbers, showing that an infinite set can be bijected to a proper subset of ...
10 votes
4 answers
802 views

How much of mathematics did Russell's paradox really break?

According to my quite likely wildly oversimplified understanding, a revolution occurred in the foundations of mathematics when Cantor's formulation of set theory was found to be inconsistent due to ...
0 votes
1 answer
126 views

In which article/book chapter did Cantor, Hibert, and Poincare formally defined or directly discussed the term “potential infinity”?

Some media sources say that "Cantor claimed that there would only be potential infinity, not actual infinity" In addition, the following link claims that Hilbert, Poincare, and Cantor were ...
26 votes
2 answers
947 views

Did Galileo's writings on infinity influence Cantor?

To what extent was Cantor motivated by Galileo's paradox? More generally, to what extent were late 19th century mathematicians motivated by, or even aware of, Galileo's paradox? This is an issue I've ...
37 votes
3 answers
3k views

What motivated Cantor to invent set theory?

I can't imagine mathematics without sets, but the question "what was mathematics like before there were sets" is not answerable, I think. Instead, a good answer to the title question should cover a ...
8 votes
2 answers
2k views

History of the definition of Injective & Surjective Function

I'm a college student, just beginning to study Elementary Set Theory. In studying about the definition of injective and surjective function, out of curiosity, it came to my mind a question about the ...
4 votes
0 answers
85 views

Kreisel on "set" as a coherent idea

In his paper Two notes on the foundations of set-theory, Kreisel begins: Recall that, naively, sets present themselves in a number of distinct contexts. [...] One may therefore doubt whether any ...
6 votes
1 answer
139 views

Were $\sigma$-algebras defined for probability?

If you want a crash course in $\sigma$-algebras and probability spaces, you should absolutely read this amazing answer by @Sycorax on Cross Validated. Sycorax says something in particular though that ...
10 votes
1 answer
244 views

Why were equivalence classes named classes rather than sets?

If $R\subseteq A\times A$ is an equivalence relation (i.e., a relation that is reflexive on $A$, symmetric, and transitive), then for each element $x\in A$, the subset $[x]_R=\{y\in A: \langle x,y\...
1 vote
1 answer
146 views

History of exponential notation for the set of functions between two sets

It's well-known that if $A$ and $B$ are two sets, then the set of all functions from $A$ to $B$ can be denoted by $B^A$: explanations of this particular notation can be found in many places: https://...
12 votes
2 answers
602 views

Were transcendental numbers considered rare, pre-Cantor?

Because the real numbers are uncountable and the real algebraic numbers are countable, there are uncountably many transcendental numbers. So there are far more transcendentals than rationals. With the ...
10 votes
1 answer
303 views

Was the continuum hypothesis commonly believed to be independent before Cohen's proof?

Someone drew my attention to the Russian translation of Rademacher and Toeplitz's Von Zahlen und Figuren (The Enjoyment of Mathematics in the English translation). In the chapter on set theory the ...
2 votes
1 answer
158 views

Who decided on the convention for ordinal multiplication?

Ordinal multiplication has always seemed backwards to me. $\alpha \times \beta$ is defined as the concatenation of $\beta$ copies of $\alpha$, not the other way 'round as one might expect. Does this ...
0 votes
1 answer
109 views

Lengths as equivalence classes

From Wikipedia on cardinal numbers: The oldest definition of the cardinality of a set $X$ (implicit in Cantor and explicit in Frege and Principia Mathematica) is as the class $[X]$ of all sets ...
4 votes
1 answer
334 views

Can we identify Paul Benacerraf in these photos

This question is about Paul Benacerraf, who worked on the philosophy of mathematics, and wrote the 1965 essay What numbers could not be (see: Benacerraf's identification problem). He was at Princeton ...
7 votes
1 answer
280 views

Was Paul Cohen a student or assistant of Gödel?

In The Man Who Loved Only Numbers, a biography about Paul Erdős, by Paul Hoffman, the author claims that Paul Cohen was "Gödel's former assistant" (p 225). However, I can't find any other sources ...
7 votes
1 answer
246 views

Who was (were) the first mathematician(s) who did not doubt the empty set?

Today there is no doubt that the empty set for the whole of mathematics is as reasonable and useful as zero for arithmetic. This however was not always the case, and surprisingly even Zermelo, who ...
0 votes
2 answers
156 views

Did Zermelo in 1914 miss the fact that there are only countably many finite strings?

Did Zermelo in 1914 miss the fact, known in 1905 already, that there are only countably many finite strings, for instance polynomials with defined parameters? He wrote: Every real or complex number $\...
-2 votes
1 answer
220 views

Endorsers of the method of well-ordering reported by Hausdorff?

In the course of preparing a lecture for graduate students about errors of early set theory I have come across this nice example reported by Hausdorff which violates Peano's successor axiom but ...
3 votes
0 answers
154 views

Details of Hilbert's proof of the continuum hypothesis [closed]

Toward the end of his paper on the infinite Hilbert sketched his proof of the continuum hypothesis. [D. Hilbert: "Über das Unendliche", Mathematische Annalen 95 (1925)] Can experts on Hilbert give ...
6 votes
4 answers
540 views

Is there a formal distinction between potential and actual infinities?

In modern set theory the difference between actual infinity and potential infinity is often not understood or even denied. Some decades back however mathematicians like Hilbert or Poincaré, let alone ...