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 Apr 18 comment How to prove that $\binom{X+L-1}{L-1} \ge (X-L\times N)^{L-1}$? Take $X = 0$ to get a counterexample when $L$ is odd Mar 28 awarded Popular Question Jan 23 answered If $\mathbb{RP}^n$ can be immersed in $\mathbb{R}^{n+1}$, how do I see that $n$ must be of the form $2^r - 1$ or $2^r - 2$? Jan 18 revised Find all triples of non-negative Integers $a,b,c$ such that $a!b!=a!+b!+c!$ deleted 7 characters in body Jan 18 answered Find all triples of non-negative Integers $a,b,c$ such that $a!b!=a!+b!+c!$ Jan 16 awarded Yearling Jan 14 comment A subset of $[0,1]\times[0,1]$ containing at most one point from each horizontal and vertical section whose boundary is $[0,1]\times[0,1]$ the map $\pi: \mathbb{R}^{2} \to [0,1)\times [0,1)$ by $\pi(x,y) = (\{x\},\{y\}).$ Jan 13 answered Determinant of the following $(n\times n)$ matrix Jan 13 answered How to proof that two lines in cube are perpendicular, without use of vectors Jan 13 comment A subset of $[0,1]\times[0,1]$ containing at most one point from each horizontal and vertical section whose boundary is $[0,1]\times[0,1]$ You really only need to show that the projection of a line with irrational slope is dense in the unit square, which follows from a standard argument. Jan 13 answered Finding the number of sequences with $0 \leq a_m \leq 3m$ Jan 13 comment Geometrical proof by induction gave a proof, then looked at answers; since David seems to have chosen explicitly not to give a full solution, I removed mine Jan 8 comment Tiling a Rectangle with integer length horizontal/vertical strips @JMoravitz - Yes, I've seen this result before and the article you linked, but I'm not sure how it would help. Thanks, though Jan 8 comment Tiling a Rectangle with integer length horizontal/vertical strips @ArchisWelankar - no, it holds in any case. Jan 8 asked Tiling a Rectangle with integer length horizontal/vertical strips Jun 22 revised Diagonals of $2n$-gon bisecting area implies? edited tags Jun 21 asked Diagonals of $2n$-gon bisecting area implies? Jun 18 awarded Tumbleweed Jun 17 comment Fundamental polygon square $abab$ He identified all of the vertices here, though, so it should only have one vertex. Also I lied about the homology; it has the same homology as that of the klein bottle Jun 17 comment Fundamental polygon square $abab$ you could look at the euler characteristic, which is zero, so if it's actually a surface, then it would be either the klein bottle or torus. unless i'm mistaken, calculating the homology (using the cellular boundary maps) makes it clear that this isn't the case, so it's not a surface.