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 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 ...
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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 ...
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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 ...
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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 ...
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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}\...
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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.
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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?
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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 ...
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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'...
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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 ...
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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-...
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How did Russell arrive at the paradox demonstrating the inconsistency of naive set theory?
As described here, we know that:
In the foundations of mathematics, Russell's paradox (also known as
Russell's antinomy), discovered by Bertrand Russell in 1901, showed
that some attempted ...
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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 ...
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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 ...
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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 ...
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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{...
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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?
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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 ...
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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 ...
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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/...
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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....
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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-...
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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 ...
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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. ...
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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 ...
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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 ...
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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 ...
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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 ...
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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&...
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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 ...
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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 ...
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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 ...
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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?
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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 ...
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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 ...
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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 ...
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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 ...
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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 ...
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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
...
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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 ...
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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 (...
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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 ...
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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 ...
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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 ...
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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 ...
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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 ...
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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 ...
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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 ...
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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\...
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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://...
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