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 5h comment A proof of a known identity using Fourier series Well, how is this sum over $n=-\infty..\infty$ defined exactly? 5h comment A proof of a known identity using Fourier series Well, yes, that's a good observation. Nevertheless, it rather says that interpreting the desired formula $\sum_{n=-\infty}^{\infty}\frac1{n+a}$ is not straightforward (if possible in any way). 5h answered A proof of a known identity using Fourier series 9h comment Representation of $(\mathbb{Z}_{\frac{*}{5}},_{\times5})$ using Cayley table Yes, that's correct, supposed you mean the 'multiplicative group of integers modulo $5$'. Also observe that $3=-2$ and $4=-1$ here, which explains the symmetry you got. 1d comment How can the axiom of choice be called “axiom” if it is false in Cohen's model? It simply means that $ZF$ implies neither $C$ nor $\lnot C$. 1d comment Direct limite commute with Direct sum Do we know something like 'the ideals $I_i$ are disjoint to all $J_j$'? 1d comment If two monoids have equivalent action categories, are they isomorphic? Considering the monoids $G$ and $H$ as categories, they will be Morita equivalent iff their idempotent completions are equivalent. Jul23 revised Quadratic form as generalized distance? added 8 characters in body Jul23 revised How does one find the image of a linear transformation, given that T is a rotation followed by a projection? added 2 characters in body Jul23 answered Quadratic form as generalized distance? Jul23 comment probability question of a set of features Note that $P(A|B)=\displaystyle\frac{P(A\cap B)}{P(B)}$ supposed $P(B)>0$. Jul23 comment probability question of a set of features Yes, @ana, that was my first thought too about this presentation of the problem. However, see Conrado Costa's answer. Observe that, as events, you listed all subsets of $\{a,b,c,d\}$. Jul21 comment Unorthodox definition of semi-abelian category Semi-abelian categories according to nLab (e.g. the category of groups) don't have to be enriched over $\bf Ab$. Jul19 answered How does one find the image of a linear transformation, given that T is a rotation followed by a projection? Jul19 comment How can I compute the infimum of the following non linear functional As the integral of an arbitrary function can be arbitrarily big in any very small interval, I would guess, the infimum would be the same ($-\frac25$), as we can approach $x^2$ by functions from $\mathcal M$, corrigating in smaller and smaller intervals... Jul19 comment How do the rows of a change of basis matrix form a basis for expressing columns? Did you read on? Tries to explain it. Jul19 comment Inquiry about My Self-Study Plan for Real Analysis (associated with my undergraduate research) I personally like that plan. But it might be 'safer' if someone would guide you (perhaps MathSE:) Jul18 comment Is the concept of a Universal Set an example of Russell's paradox? As far as we don't have other things but sets, yes: Let $U$ be the union of all sets and $V$ be the set of all sets. If $x$ is a set, then so is $\{x\}$, and hence $x\in\{x\}\subseteq U$. On the other hand, if $x\in U$, then $x$ is an element of a set, hence is a set by initial hypothesis, so $x\in V$. Jul18 comment Fibonacci $\equiv -1 \mod p^2$ How you prove for a prime \$3