Jon
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 Jun 8 awarded Caucus May 17 awarded Popular Question Feb 22 comment If $A,B\in M(2,\mathbb{F})$ and $AB=I$, then $BA=I$ The downvote was from me. Though what you have written is mathematically correct, it does not answer the OP's question as stated. Feb 20 awarded Nice Question Feb 2 answered Is there a “canonical” representation of integers using numbers other than primes? Jan 28 comment Find members of this field. To find -1 in $\mathbb{Z}_5$, recall that the symbol "-1" stands for the (unique) element which, when added to 1, yields zero. You only have five possibilities to check. (The problem of finding 1/3 in $\mathbb{Z}_7$ is similar.) Jan 16 comment truth table equivalency I believe that ~ is the "not" operator. Dec 14 awarded Yearling Dec 13 awarded Civic Duty Dec 3 awarded Enlightened Dec 3 awarded Nice Answer Nov 29 comment functional equation uniqueness $f(x^{2})= f(x)^{2}$ in $\mathbb{C}$ and $f(x)+f''(x) = 0$ in $\mathbb{C}$ @ccc: the problem statement requires that $f$ be holomorphic. Nov 14 comment Was it an even deal for me? Completely changing the question after posting it (without leaving any hint that the question has changed) is considered bad form. Sep 28 accepted Why are the centers of $R$ and $\text{End}_{\text{Ab}}(R)$ isomorphic? Sep 28 revised Why are the centers of $R$ and $\text{End}_{\text{Ab}}(R)$ isomorphic? added 157 characters in body Sep 27 revised Why are the centers of $R$ and $\text{End}_{\text{Ab}}(R)$ isomorphic? added 123 characters in body Sep 27 comment Why are the centers of $R$ and $\text{End}_{\text{Ab}}(R)$ isomorphic? @Pierre-Yves Gaillard: Thanks for the suggestion. I have added the author's name. The book is part of the Graduate Studies in Mathematics series. Sep 27 revised Why are the centers of $R$ and $\text{End}_{\text{Ab}}(R)$ isomorphic? added 16 characters in body Sep 27 revised Why are the centers of $R$ and $\text{End}_{\text{Ab}}(R)$ isomorphic? edited body Sep 27 comment Why are the centers of $R$ and $\text{End}_{\text{Ab}}(R)$ isomorphic? Well that's strange. I can't see any error in what you wrote; have I misunderstood the exercise? Here is the text exactly as it appears: "2.17. Let $R$ be a ring, and let $E = \text{End}_{\text{Ab}}(R)$ be the ring of endomorphisms of the underlying abelian group $(R, +)$. Prove that the center of $E$ is isomorphic to the center of $R$."