Matti Åstrand
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 May5 comment What is the proper name of this class of rings? I guess I would just call it "an integral domain of characteristic 0"... But your statement about polynomials is not true: $R$ could also be an infinite integral domain of characteristic $p$. May1 comment I need to diagonalize this matrix but I'm not sure it can be It can't be diagonalized, since the matrix only has one eigenvector for the double eigenvalue. You should check out "Jordan Normal Form". May1 answered Is the following problem convex? May1 comment Is the following problem convex? It's not true in general that a composition of two convex functions is convex. See this question Mar25 answered Is there a property that isolates the formulas that remain valid as you move from the natural numbers to the integers? Mar14 comment Shortest string possible I would think it has to be 0100010. The shortest one can't have a substring that's also an instance of S. Mar14 comment Count indices in summation I think inclusion-exclusion principle might help you. Jul28 awarded Yearling Jul16 awarded Nice Answer Jul29 awarded Editor Jul29 revised Why is the “finitely many” quantifier not definable in First Order Logic? Correction. Jul28 awarded Teacher Jul28 answered Why is the “finitely many” quantifier not definable in First Order Logic? Jul27 awarded Supporter