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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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27 votes
2 answers

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 ...
Dave L Renfro's user avatar
9 votes
2 answers

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 ...
user avatar
41 votes
3 answers

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 ...
Ben's user avatar
  • 802
17 votes
1 answer

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. ...
quiet's user avatar
  • 273
15 votes
1 answer

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 ...
user4894's user avatar
  • 1,345
14 votes
0 answers

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 ...
Franz Kurz's user avatar
13 votes
3 answers

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 ...
Joseph O'Rourke's user avatar
5 votes
3 answers

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
11 votes
1 answer

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
9 votes
2 answers

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 ...
Gin99's user avatar
  • 99
8 votes
1 answer

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
6 votes
4 answers

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 ...
Franz Kurz's user avatar
5 votes
1 answer

Where did Borel stress that $\mathbb{Q}$ being effectively enumerable by $\mathbb{N}$ is not about its size?

In the book 'Practical Foundations of Mathematics' (Paul Taylor), available online, one reads: As Emile Borel stressed in 1908, the important observation about $\mathbb{Q}$ [that there is a ...
weakmoons's user avatar
  • 151
5 votes
1 answer

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 ...
user51309's user avatar
  • 205
4 votes
0 answers

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

First use of curly braces to denote a set?

I was wondering who was the first person to Use curly braces to represent a finite set. Exempli gratia, $\{1,2,3\}$. Use set builder notation. Such as $\{2n:n \in \mathbb{Z}\}$ to represent the even ...
yberman's user avatar
  • 173
0 votes
0 answers

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