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Mathematics
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mathcounterexamples.net
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I'm living in Paris, France and doing Math as a hobby, with special interest in Mathematical logic and Analysis.

I opened in July 2014 a website dedicated to Math Counterexamples. I welcome any suggestion for additional counterexamples... at least at a level that I can understand!

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Top Posts (1,131) All Questions Answers | Votes Newest

28 Group $G$ whose center $Z(G)$ is cyclic and with $G/Z(G)$ commutative Jun 28 '15
20 Proof: Is there a line in the xy plane that goes through only rational coordinates? Dec 12 '15
19 Proof that the number of proofs is countably infinite Jun 11
17 Is $F=\left\lbrace f: f\in C_{\left[0, 1\right]}, f\left(0\right)=f\left(1\right)\right\rbrace$ complete metric space? Jun 28
16 Convergence of infinite sum (factorial and root) Nov 22 '16
13 Find $\lim\limits_{x\to \infty} \frac{x\sin x}{1+x^2}$ Jun 10 '15
12 L'Hôpital's rule: number of iterations… May 26
12 Differentiability of a two variable function $f(x,y)=\dfrac{1}{1+x-y}$ Aug 22 '15
11 Find the value $\int_{0}^{1}f(x) \,\mathrm dx$ without words Aug 13
11 Computing $(1+\cos \alpha +i\sin \alpha )^{100}$ Dec 11 '15
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