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593
votes
What's a mathematician to do?
Not theorems, by themselves. Is there, for example any real reason that even such famous results as Fermat's Last Theorem, or the Poincaré conjecture, really matter? …
462
votes
Awfully sophisticated proof for simple facts
Irrationality of $2^{1/n}$ for $n\geq 3$: if $2^{1/n}=p/q$ then $p^n = q^n+q^n$, contradicting Fermat's Last Theorem. Unfortunately FLT is not strong enough to prove $\sqrt{2}$ irrational. …
378
votes
Widely accepted mathematical results that were later shown to be wrong?
$
Many mathematician's gut reaction to the question is that the answer must be yes and Minkowski's uniqueness theorem provides some mathematical justification for such a belief---Minkwoski's uniqueness … theorem implies that an origin-symmetric star body in $\mathbb{R}^n$ is completely determined by the volumes of its central hyperplane sections, so these volumes of central hyperplane sections do contain …
325
votes
Awfully sophisticated proof for simple facts
But $$\int_{\bf R} \lim_{n \to \infty} f_n(x)\ dx = 0 \neq 1 = \lim_{n \to \infty} \int_{\bf R} f_n(x)\ dx,$$ contradicting the dominated convergence theorem. …
263
votes
What are the most misleading alternate definitions in taught mathematics?
Theorems,
questions, exercises, examples as well as definitions can be coming
from an incorrect view of a subject! …
260
votes
Accepted
Consequences of the Riemann hypothesis
What he needed from GRH is the lack of real zeros in the interval $(53/54,1)$.
m) Removing a condition in the Brauer-Siegel theorem. … That is, GRH implies the Brauer-Siegel theorem holds for sequences of number fields $K_n$ fitting condition (i).
n) Lower bounds on root discriminants. …
260
votes
Accepted
What are "perfectoid spaces"?
Now let me just briefly summarize the main theorems on the basic nature of perfectoid spaces. … This leads to an improvement on Faltings's almost purity theorem:
Theorem: Let $R$ be a perfectoid $K$-algebra, and let $S/R$ be finite étale. …
251
votes
Most interesting mathematics mistake?
It is a counterexample to an 1899 "Theorem" of C.N. Little (Yale PhD, 1885), accepted as true by P.G. … The Perko pair have different writhes, and so Little's "Theorem", if true, would prove them to be distinct! …
247
votes
Best algebraic geometry textbook? (other than Hartshorne)
It is a very complete book even introducing some needed commutative algebra and preparing the reader to learn arithmetic geometry like Mordell's conjecture, Faltings' or even Fermat-Wiles Theorem. … As a fundamental complement check Hauser's wonderful paper on the Hironaka theorem. …
240
votes
Accepted
Is the analysis as taught in universities in fact the analysis of definable numbers?
Tarski's theorem on the
non-definability of
truth
shows that there is no first-order definition that allows
us a uniform treatment of saying that a particular
particular formula $\varphi$ is true at a … In recent work (soon to be submitted for publication),
Jonas Reitz, David Linetsky and I have proved the following
theorem:
Theorem. …
237
votes
Awfully sophisticated proof for simple facts
Seen on https://legauss.blogspot.com/2012/05/para-rir-ou-para-chorar-parte-13.html
Theorem: $5!/2$ is even.
Proof: $5!/2$ is the order of the group $A_5$. … But the Feit-Thompson Theorem asserts that every finite group with odd cardinal is solvable, so $5!/2$ must be an even number. …
233
votes
Accepted
What makes dependent type theory more suitable than set theory for proof assistants?
They produce complex webs of definitions, theorems, and constructions, therefore $V$ should support management of large collections of formalized mathematics. … For instance, saying that a body of mathematics is "just a series of definitions, theorems and proofs" is a naive idealization that works in certain contexts, but certainly not in practical formalization …
232
votes
Accepted
Is there an introduction to probability theory from a structuralist/categorical perspective?
Irving Segal proved in “Equivalences of measure spaces” (see also Kelley's “Decomposition and representation theorems in measure theory”)
that for an enhanced measurable space $(S,M,N)$ that admits a faithful … The best argument for such restrictions is the following Gelfand-type duality theorem for commutative von Neumann algebras.
Theorem.
The following 5 categories are equivalent. …
226
votes
Widely accepted mathematical results that were later shown to be wrong?
See Theorem 1 in Cours D'Analyse Chap. VI Section 1. Five years later Abel pointed out that certain Fourier series are counterexamples. … See Graviton's answer for another assessment of Cauchy's work, which operated with continuity using infinitesimals in such a way that Abel's counterexample was not a counterexample to Cauchy's theorem. …
226
votes
Accepted
Why doesn't mathematics collapse even though humans quite often make mistakes in their proofs?
If mathematics were done by computers that mindlessly searched for theorems and proof but sometimes made mistakes in their proofs, then I expect that it would collapse. … For instance, while working on a recent project I discovered no fewer than nine mistaken theorem statements (not just mistakes in proofs of correct theorems) in published or almost-published literature …