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Questions tagged [set-theory]

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

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Was such advanced content on set theory taught in American elementary schools back in 1965?

The image attached is a comic strip from "Peanuts," dating back to 1965. It portrays Sally, the younger sister of Charlie Brown, throwing a tantrum over learning set theory in elementary ...
enjin2000's user avatar
3 votes
1 answer
282 views

Who is William Bigelow Easton?

William Bigelow Easton is the full name of the American mathematician who is the eponym of Easton's theorem, a far-reaching application of the method of forcing in set theory. Despite the many ...
Todd Trimble's user avatar
1 vote
1 answer
123 views

Who first proved that empty set is subset of all sets?

Who is the mathematician who proved that empty set is subset of all sets and made it known to most mathematicians? I looked into the ripple effects in the mathematical world that would occur if the ...
user1274233's user avatar
2 votes
1 answer
86 views

Equicardinality of $\mathbb{R}$ and $\mathbb{R}^2$ via interleaving decimal expansions

As Fernando Q. Gouvêa notes in his paper, Was Cantor Surprised? (Amer. Math. Monthly 118 (March 2011), 198–209) Cantor initially tried to prove that $(0,1]$ and $(0,1] \times (0,1]$ have the same ...
Timothy Chow's user avatar
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4 votes
2 answers
774 views

When and why was the concept of "having a least upper bound" dubbed "completeness", as in Axiom of Completeness?

The Axiom of Completeness states that any non-empty set with an upper bound has a least upper bound. When and why was this concept of least upper bound dubbed "completeness"? It's true, of ...
SRobertJames's user avatar
2 votes
0 answers
109 views

What were Cantor’s “real numbers of higher type”?

In the preamble to “Essays on the Theory of Numbers”, Dedekind makes passing reference to a theory (expounded in Cantor’s “Ueber die Ausdenung eines Satzes aus der Theorie der trigonometrischen Reihen”...
James Propp's user avatar
1 vote
0 answers
83 views

Whence Whitehead's essence?

In the article Quine’s New Foundations of The Stanford Encyclopedia of Philosophy (Summer 2019 Edition), Thomas Forster writes: In [1944] Hailperin gave the first of a number of finite ...
Frode Alfson Bjørdal's user avatar
13 votes
1 answer
1k views

What was the motivation for the choice of the subset symbol?

I gather that the symbols $\subset$ and $\supset$ were introduced by Ernst Schröder in his 1890 Vorlesungen über die Algebra der Logik. This account also appears—attributed to good old Cajori—in an ...
Paul Tanenbaum's user avatar
1 vote
1 answer
180 views

Was "potency set" used for power set?

Cross posted at Math Overflow For historical reasons, the English term "power set" in set theory is a translation of the German "Potenzmenge", which is still in use in German ...
Frode Alfson Bjørdal's user avatar
4 votes
0 answers
179 views

Who proposed terminating decimals as a major set and why are them important in France?

After looking at some school sources in French, it is common to provide the various number sets in the following order $$\mathbb{N}\subset \mathbb{Z}\subset\mathbb{D}\subset\mathbb{Q}\subset\mathbb{R}\...
Mauricio's user avatar
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Who was the first to use bijections?

I know that Bourbaki were the first who used the word 'bijection', but one-to one functions were for sure used before them. So do you aware of the earliest examples of one-to-one correspondences?
kerzol's user avatar
  • 101
5 votes
1 answer
641 views

Was Gottlob Frege hospitalized by Russell's Paradox?

After receiving the infamous letter from Bertrand Russell, Gottlob Frege allegedly had a mental breakdown and had to be hospitalized. I've seen various informal references to this, such as: Russell's ...
Ray Butterworth's user avatar
6 votes
1 answer
464 views

Cantor, set theory and foundations

Did Georg Cantor ever think that set theory could serve as a foundational system for all of mathematics? He died in 1918, but Zermelo set theory (just Z, no ZF or ZFC yet) was described in a paper by ...
Alex's user avatar
  • 275
2 votes
0 answers
92 views

Was there a view of a figure as a set of points before set theory?

A circle can be written as the solution set of an equation $x^2+y^2=1$. I have heard that Fermat associated figures with equations in the 17th century. Did people see figures as sets of points before ...
BonBon's user avatar
  • 151
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0 answers
60 views

What are Gödel's property theories

The opening sentence of Roger Myhill's article Paradoxes, in Synthese 60 (1984), 129-143, is: “Gödel said to me more than once "There never were any set-theoretic paradoxes, but the property-...
Frode Alfson Bjørdal's user avatar
2 votes
0 answers
149 views

Zermelo's or Fraenkel's early consideration of something equivalent to countable Replacement

I have now claimed a few times on the internet, based on something (sensible!) I read, that at some point in the 1920s, that Zermelo at one point considered as a set theoretic axiom (schema) something ...
David Roberts's user avatar
1 vote
1 answer
138 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{...
TonyK's user avatar
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4 votes
1 answer
159 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/...
TonyK's user avatar
  • 345
2 votes
0 answers
97 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....
Sam Sanders's user avatar
3 votes
0 answers
229 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-...
TonyK's user avatar
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0 votes
1 answer
183 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.
TonyK's user avatar
  • 345
6 votes
1 answer
437 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 ...
modnar's user avatar
  • 575
11 votes
1 answer
2k 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 ...
Rax Adaam's user avatar
  • 484
8 votes
1 answer
350 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&...
Rax Adaam's user avatar
  • 484
2 votes
0 answers
107 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 ...
TransfiniteGuy's user avatar
13 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 ...
10GeV's user avatar
  • 259
4 votes
0 answers
148 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 ...
Mozibur Ullah's user avatar
3 votes
1 answer
759 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 ...
Alex's user avatar
  • 275
3 votes
2 answers
289 views

In which article/book chapter did Cantor, Hilbert, and Poincaré formally define or directly discusse 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, Poincaré, and Cantor were ...
High GPA's user avatar
  • 133
0 votes
0 answers
372 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 ...
Franz Kurz's user avatar
4 votes
0 answers
89 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 ...
Noah Schweber's user avatar
6 votes
1 answer
196 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 ...
gen-ℤ ready to perish's user avatar
11 votes
1 answer
324 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\...
evenodd's user avatar
  • 213
1 vote
1 answer
216 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://...
user6530's user avatar
  • 3,870
12 votes
2 answers
1k 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'...
jmarvin_'s user avatar
  • 121
8 votes
1 answer
385 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 ...
modnar's user avatar
  • 575
3 votes
0 answers
157 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 ...
user avatar
10 votes
1 answer
339 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 ...
AnatolyVorobey's user avatar
5 votes
3 answers
781 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 ...
user525966's user avatar
0 votes
1 answer
117 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 ...
Hans-Peter Stricker's user avatar
2 votes
1 answer
314 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 ...
user157860's user avatar
4 votes
1 answer
403 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 ...
David Roberts's user avatar
2 votes
1 answer
168 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 ...
user4894's user avatar
  • 1,345
9 votes
1 answer
421 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 ...
Kevin Long's user avatar
9 votes
1 answer
323 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 ...
Franz Kurz's user avatar
6 votes
2 answers
619 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 ...
Franz Kurz's user avatar
0 votes
2 answers
165 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 $\...
Franz Kurz's user avatar
-2 votes
1 answer
225 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 ...
Franz Kurz's user avatar
3 votes
0 answers
158 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 ...
Franz Kurz's user avatar
4 votes
1 answer
377 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 (...
Franz Kurz's user avatar