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 Jan 14 answered If the $81$ digit number $111\cdots 1$ is divided by $729$, the remainder is? Jan 13 accepted Computational Topology and Lie Group Theory Jan 13 comment Computational Topology and Lie Group Theory @PeterFranek There's also "Elementary Applied Topology" by R. Ghrist. Jan 12 comment Computational Topology and Lie Group Theory I'm not working right now because of a serious (but hopefully in remission) illness so I've plenty of time on my hands. I've always wanted to study math more seriously. Jan 12 asked Computational Topology and Lie Group Theory Jan 10 comment Finding the inverse of $H-G E^{-1}F$ @Vim $M/E = H-G E^{-1}F$ appears in the "partitioned inverse formula" which gives the inverse of a partitioned matrix, so I thought it was always invertible and I didn't even look for easy counterexamples. The theorem just says "assume $E$ and $H$ are invertible". Jan 10 asked Finding the inverse of $H-G E^{-1}F$ Dec 31 awarded Commentator Dec 31 accepted Monochromatic cycle in graph Dec 31 comment Monochromatic cycle in graph The only result I figured out on my own is lemma 3.1! I'd have never solved this "riddle" on my own. Dec 31 comment Monochromatic cycle in graph @GregoryJ.Puleo I don't know any theory about these things so I tried to prove it from scratch (it's a riddle I found somewhere). I know there are at least 14 edges of the same color and if those connect only 6 vertices then we can certainly find a cycle of length 6. But if the 14 edges connect 7 or 8 vertices things get complicated. After a while I gave up. Dec 31 revised Monochromatic cycle in graph added 100 characters in body Dec 31 asked Monochromatic cycle in graph Dec 15 comment Lattice Paths with no more than k consecutive steps Keep in mind the generalized inclusion exclusion principle. It might help you with your problem. Dec 15 revised How would you show that $Ax=b$ has a solution $\iff \text{rank } A = \text{rank } [A\, b]$? added 9 characters in body Dec 15 answered How would you show that $Ax=b$ has a solution $\iff \text{rank } A = \text{rank } [A\, b]$? Nov 25 revised Minimization of Expected Value added reference to book Nov 25 awarded Teacher Nov 25 accepted Minimization of Expected Value Nov 25 answered Minimization of Expected Value