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 Jan 2 comment Are there real-life relations which are symmetric and reflexive but not transitive? Surely this relation is not reflexive for newborns... Dec 29 comment How to prove that something is definable or not definable in a given structure?! Dear André, I am currently doing a little undergraduate research project in o-minimal structures. Thank you for showing me that this is actually something more people know about :P Dec 28 comment A challenge by R. P. Feynman: give counter-intuitive theorems that can be translated into everyday language This theorem would fail Feynman's judgement for the same reason that Banach-Tarski is not an example. Dec 27 comment Consider the sequence 01110100… Induction?[filler] Dec 26 comment The cardinality of $\mathbb{R}/\mathbb Q$ Awesome.[filler] Dec 26 comment The cardinality of $\mathbb{R}/\mathbb Q$ So why exactly are they both size continuum? Dec 25 comment Rouche's theorem So... what did you try? Dec 24 comment Studying Math, All Over Again With all due respect, Khan is not mathematics. Khan is a list of courses in passing exams. Dec 23 comment Finding $\lim_{x\to \pm\infty}f(x)$ where $a,b>0$ It's bounded from above by $(a+b)/2$ Dec 23 comment Question about dynamical behavior near point What are your own thoughts... Dec 22 comment Graph of functions That's not what you asked for. Dec 22 comment Graph of functions wolframalpha.com Dec 22 comment Supremum of continuous functions is continuous? What is $H^1(\Omega)$? Forgive my lack of knowledge of functional analysis. Dec 22 comment Maximum absolute deviation Dear Juan, you really need to work on your mastery of the English language if you want useful comments. Many of your questions are hard to understand, and I, for one, do not understand what you want from us in this question. Could you rephrase it? Dec 22 comment how to make a matrix a magic square? There are many "matrix problems". Could you change the title to something more useful, such as "how to make a matrix a magic square" Dec 22 comment Algebra question resubmited @DavidMitra: only because of the later edits by Crete and amWhy after my comment, and the question is still not clear to me. Dec 22 comment Differential Equation And if you're editing anyway, use MathJax: meta.math.stackexchange.com/questions/5020/… Dec 22 comment Differential Equation Integrate what twice? Please clarify your question to get more useful comment and help. Dec 22 comment Differential Equation Well yes, that clearly is your question, but what approach are you trying, because I don't think this is very clear from what you wrote. Dec 22 comment Differential Equation In that case, what are you trying to do (in terms of equations)?