Unanswered Questions
700 questions with no upvoted or accepted answers
20
votes
0answers
32k views
Who first defined the “equal-delta” or “delta over equal” ($\triangleq$) symbol?
The symbol $\triangleq$ is sometimes used in mathematics (and physics) for a definition. It is instantiated for instance in the Unicode Character 'DELTA EQUAL TO' (U+225C).
The notation $t \triangleq ...
20
votes
0answers
531 views
What is the modern significance of Theaetetus's classification of quadratic irrationals?
Before Eudoxus's theory of proportion there was a theory of irrationals based on continued fraction expansions, which Fowler calls anthyphairesis. Theaetetus is said to develop a classification of ...
17
votes
0answers
700 views
Did Kontsevich start a lecture with “one I will not define, the other nobody knows how to define, and we will be proving that they are equivalent”?
The story was circulating in early 2000s, so presumably it happened in 1990s. Kontsevich, it goes, opened a lecture course on mirror symmetry with:"This course is about two categories. One I will not ...
16
votes
0answers
538 views
When did people know that all real polynomials of degree greater than 2 are reducible?
Admittedly, this may not be a research level question, but I am deeply curious about this.
Let $f(x) \in \mathbb{R}[x]$, and write $d = \deg f$. It is well known that if $\deg f > 2$, then $f$ is ...
15
votes
0answers
489 views
Conditionally convergent series
I am looking for the original reference discussing a specific, elementary example of a rearrangement of series converging to a value different from the original series. In what follows, I give some (...
14
votes
0answers
400 views
A basic mistake by Cayley
Arthur Cayley's first paper on abstract groups, in 1854, can be found in his Collected Papers on the Internet Archive, starting at https://archive.org/stream/collectedmathema02cayluoft#page/122/mode/...
12
votes
0answers
267 views
Who was that forgetful mathematician?
Who was the (Japanese?) mathematician who said in a lecture that a certain conjecture still remained to be proved, and one of the students present told him that he (the mathematician) had already ...
12
votes
0answers
269 views
What was the typical format of a 16th century mathematical debate?
In The Equation that Couldn't be Solved, Mario Livio writes of academia in 16th century Bologna. Apparently, mathematicians would take part in public debates, sometimes involving solving problems. ...
12
votes
0answers
125 views
Did Walter Pitts refuse to allow his name to be made publicly available?
I read on the Wikipedia page on Walter Pitts that :
Pitts was also described as an eccentric, refusing to allow his name
to be made publicly available. He refused all offers of advanced
...
11
votes
0answers
72 views
Why are the classic statistical approaches to NLP mostly generative models while the most recent ones are mostly discriminative?
Looking at the classic statistical approaches to natural language processing (e.g. tagging, parsing, etc.), I see that they are mostly generative models: n-gram models, Naive Bayes classifiers, hidden ...
10
votes
0answers
288 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 ...
10
votes
0answers
3k views
How did Jun John Sakurai die?
How did theoretical physicist Jun John Sakurai die? The only result from extensive googling is that he died "suddenly" while working at CERN. Does anyone know anything more specific?
9
votes
0answers
176 views
First use of term “Hilbert's Nullstellensatz”
This year (2021) marks the 100th anniversary of Emmy Noether's 1921 paper in which she introduced Noetherian rings and proved the primary ideal decomposition for them. The original version of her ...
9
votes
0answers
364 views
Whence “homomorphism”, “homomorphic”?
The kernel question leads to another : Today, homomorphism (resp. isomorphism) means what Jordan (1870) had called isomorphism (resp. holoedric isomorphism). How did the switch happen?
“Homomorphic” ...
9
votes
0answers
715 views
Ramanujan's Method for solving cubic, quartic, quintic
In Ramanujan's Notebooks Volume IV pg. 31 by Bruce C. Berndt, he describes an easy way to solve the general quartic by starting with the system$$x^2+ay=b\\y^2+cx=d\tag1$$
And solving for $x$; which ...
