Ricky Bobby
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 Feb 28 comment Let $f(x,y)$ be a function of two variables such that $\displaystyle\lim_{(x,y)\to(0,0)}=5$. Which is true? (b) [...] $f(x,y)$ approaches 5 but NOT REACHING (<- false) 5. Nov 9 comment linear operator on a vector space V such that $T^2 -T +I=0$ Is it true for a vector space with not a finit dimension ? Nov 6 comment What kind of quadrilateral is determined by four sides and a diagonal? @DavidZaslavsky I added a very quick proof for a convex polygon, and your question prove that it's not true for not convex simple polygons. May 14 comment Dealing with connectness and compactness of matrices. @srijan ... I have some books at home but no links. For a start wikipedia should be fine (look at the references) and the example from Michael Hardy should help a lot. May 14 comment Dealing with connectness and compactness of matrices. @srijan With the right norm you can easily prove the compactness, and with the right continuous function the connectedness. "The only continuous functions from X to {0,1} are constant" this property is commonly use to prove connectedness May 14 comment Dealing with connectness and compactness of matrices. @srijan You should try to familiarize yourself with different common norms on matrices, and functions (like the determinant). Then you will have most of the tools to solve this kind of problems. May 14 comment Dealing with connectness and compactness of matrices. you should have a look at your math classes, and if you don't have one articles on wikipedia to find all the way you can solve such a problem. For compactness, if I remember what I've learn 8 years ago, in a finite space ou can easily use the sequential definition to prove that it's closed and bounded. (for example with n=1, the set of all symmetric positive matrices is similar to R+ => not bounded and therefore not compact) Oct 28 comment Truth and undecidability @AsafKaragila, that's a surprising coincidence, I was discussing with a friend about this question (truth and indecidability) just half an hour ago, and your comment is pretty much the answer we were looking for ! Thx a lot Asaf. Oct 10 comment Truth and undecidability @LostInMath yes,thx, I answered your comment before looking at Levon's answer. but Levon's answer perfectly answered my question Oct 10 comment Truth and undecidability okay thx a lot, I am going to have a look at it Oct 10 comment Truth and undecidability Thx, I guess this is a good start, but can you define a little bit more wath you mean by structure ? Oct 10 comment Truth and undecidability @LostInMath I'm saying that S can be true but not provable, so I am not talking aboout truth in term of logical consequence of T. For example when I say that all even number > 2 can be written as the sum of 2 prime numbers, It might be true (if I test every single even number) but It might be not provable (If there is no proof and the only way is to test every odd number and testing an infinit number of values isn't a proof). So how would you express this kind of truth ? Aug 24 comment Composition of permutation to generate all permutations Thanks I created a new question, you might want to migrate your answer there ? Aug 24 comment Composition of permutation to generate all permutations thanks a lot for your answer, the question is a little bit different, I clarified it. Aug 24 comment Composition of permutation to generate all permutations thanks a lot for your answer, the question is a little bit different, I clarified it. Aug 17 comment Are some real numbers “uncomputable”? Thanks a lot for all your answers, it raises very interesting concepts and notions. Jul 23 comment Factorial decomposition of integers? @Olivier, I actually thinking of a mapping between n! and all permutation, and I should have used that as a proof. But since I couldn't find anything on the web about that I had the feeling something was wrong ... :D! Jul 23 comment Factorial decomposition of integers? I was actually thinking about permutation when this question came to my mind, I didn't thought about using it to prove the decomposition. thanks a lot for your answer. Jul 18 comment indecidability, independency and company @Theo @Asaf ,thx Jul 18 comment indecidability, independency and company Thanks a lot! that's exactly what I was looking for.