Peter Taylor
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 Jan 24 comment The hardest game of mahjongg I think you need to address the issue of how to lay out the tiles for arbitrary $n$ before it even makes sense to start thinking about an answer. Jan 15 comment Maximal tiling without any 3-in-a-rows @randomra, if the maximum Hamming weight which can be achieved in an $m\times n$ rectangle is $w$ then that gives an upper bound for the density of any infinite tiling of $\frac{w}{mn}$ by the simple mechanism of superimposing an $m \times n$ grid over the infinite tiling. Jan 12 awarded Yearling Jan 9 comment Maximal tiling without any 3-in-a-rows The existence of (non-tiling) moderately large squares with densities > 1/2 (e.g. 15x15 with 114 bits set) indicates that the case analysis would have to work on larger units than those squares. I very much doubt that the number of cases for this type of approach would be computationally tractable. Jan 9 comment Maximal tiling without any 3-in-a-rows I don't understand the argument that cases can be eliminated by the symmetry of swapping 0s and 1s: that's not a symmetry, because 000 is allowed and 111 isn't. I also don't understand what contradiction you see in your first example. Jan 9 revised Maximal tiling without any 3-in-a-rows added 75 characters in body Jan 8 revised Maximal tiling without any 3-in-a-rows deleted 243 characters in body Dec 12 comment If $x^n$ is ivertible in a ring show that $x$ is invertible. So to be precise, your question is how to show that, given a left inverse of $x$ and a right inverse of $x$, the two must be the same even in a non-commutative ring? Nov 30 comment Erdős and Szemerédi sums and producs Note: this looks suspiciously like a certain active contest. Nov 28 reviewed Reject Find the Probability mass function(a grid with p-values in the cells) Nov 28 reviewed Close First Order Logic problem with Compactness theorem Nov 28 reviewed Close formula for series the 0,1,0,1,0,1,… With certain laws Nov 28 reviewed Close Probability that two independent samples, each one without repetition, share K elements Nov 28 reviewed Close Verifying that $T_0 = F, T_n = 0$ is a universal $\delta$-functor Nov 28 reviewed Close On the meaning of “or” in logic Nov 28 answered name or characterization for the “partition” lattice of integer partitions of some n? (Young lattice row partial order) Nov 27 answered Maximal tiling without any 3-in-a-rows Nov 18 reviewed Close Is the graph of $xy=1$ in $\mathbb C^{2}$ connected? Nov 18 reviewed Close Limit value of a sequence Nov 13 reviewed Close Find the center and radius of the circle whose equation is $x^ 2 + y^ 2 - 6x - 2y + 4 = 0$