José Carlos Santos

Porto, Portugal

http://www.fc.up.pt/mp/jcsantos/

I am a mathematician who works at the University of Porto (Portugal). My PhD, on Representation Theory, was obtained at the Université Paris — Denis Diderot, in 1996.

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Why was "An Update to our Community and an Apology" deleted?

discussion meta deleted-questions stack-exchange-team censor asked Dec 24, 2019 at 12:16

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130 votes

Unexpected examples of natural logarithm

soft-question logarithms big-list asked Jul 3, 2017 at 13:07

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61 votes

Proving $\left(1-\frac13+\frac15-\frac17+\cdots\right)^2=\frac38\left(\frac1{1^2}+\frac1{2^2}+\frac1{3^2}+\frac1{4^2}+\cdots\right)$

real-analysis sequences-and-series summation asked Oct 2, 2017 at 10:17

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48 votes

Why were the Allies so much better cryptanalysts?

world-war-two espionage cryptology secrecy asked Nov 22, 2020 at 9:03

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31 votes

Could a German insult Hitler without being arrested?

nazi-germany hitler asked Dec 15, 2019 at 10:02

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30 votes

In what way were Renaissance battles like chess matches?

middle-ages warfare renaissance reference asked Oct 29, 2019 at 17:55

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28 votes

Is every matrix conjugate to its transpose in a continuous way?

linear-algebra matrices continuity transpose similar-matrices asked Dec 14, 2018 at 10:03

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27 votes

How likely it is that a nobleman of the eighteenth century would give written instructions to his maids?

united-kingdom 18th-century education asked Jan 24, 2021 at 12:00

history.stackexchange.com

26 votes

Change in the way the first posts review queue works?

support bug status-completed review asked Apr 15, 2021 at 7:42

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25 votes

Constructing the reals from the integers

reference-request real-numbers asked Aug 25, 2017 at 14:41

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Top Answers

186

Why not include as a requirement that all functions must be continuous to be differentiable?

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How can a "proper" function have a vertical slope?

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Does an increasing sequence of reals converge if the difference of consecutive terms approaches zero?

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Can a binary operation have an identity element when it is not associative and commutative?

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Unsolved Problems due to Lack of Computational Power

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Why a $20$ digit number starting with eleven $1$'s cannot be a perfect square?

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False proof that $ρe^{iθ} = ρ$ and so complex numbers do not exist?

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What is an example of a sequence which "thins out" and is finite?

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How many times do you have to use L'Hôpital's rule?

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How are the known digits of $\pi$ guaranteed?

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If derivative of $f$ is continuous, then $f$ is continuous.

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Can we use symmetry rules in improper integrals?

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Why is the notion of analytic function so important?

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How to determine if a set of five $2\times2$ matrices is independent

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Problem with estimating a sequence with intuition

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A Simple Calculus view on Fermat's Last Theorem

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Cross product in higher dimensions

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Understandable questions which are hard for non-mathematicians but easy for mathematicians

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Non abelian group which contains no abelian subgroup

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Can the product of three complex numbers ever be real?

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Integration of secant

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Are these square matrices always diagonalisable?

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Sets that are both Sum-free and Product-free

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Story of a student who solves an open problem

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Finding the 10th root of a matrix

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How could $\varnothing$ be unique if it could be vacuously false?

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General request for a book on mathematical history, for a VERY advanced reader.

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How to compute the determinant of this Toeplitz matrix?

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What is the context for Napoleon's quote "[the Austrians] did not know the value of five minutes"?

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Why does Zorn's Lemma fail to produce a largest group?

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