Marius Buliga
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 Jul 2 awarded Curious Jun 25 awarded Yearling Apr 24 answered Oriented Reidemeister move R2d by splices and loop adding/erasing? Apr 24 comment Oriented Reidemeister move R2d by splices and loop adding/erasing? Correction: "This would mean that the order of applications of splices 1/2 and loop 1/2" ... is commutative. Apr 24 comment Oriented Reidemeister move R2d by splices and loop adding/erasing? Thanks, I'll try. But is not obvious that the spliced form is invariant. This would mean that the order of applications of splices 1/2 and loop 1/2. Notice that all moves go in both directions and one may obtain complex diagrams from simple ones. In case anybody interested, what is not clear at all to me is what happens if we work not with tangle diagrams, which are globally planar graphs, but with "locally planar" tangle diagrams, i.e. we allow the possibility that two edges of the diagram cross without counting this a real crossing. Apr 23 asked Oriented Reidemeister move R2d by splices and loop adding/erasing? Oct 4 comment When a semigroup extension $S \times A$ of a semigroup $S$ with a commutative group $A$ contains a copy of $S$? No, I've seen both names used for both objects, it's like $\mathbb{N}$, which contains or not $0$, according to pedagogical school of thought. Oct 2 comment When a semigroup extension $S \times A$ of a semigroup $S$ with a commutative group $A$ contains a copy of $S$? Thank you, I have not realized that trivially the example 2 is a direct product. Oct 2 accepted When a semigroup extension $S \times A$ of a semigroup $S$ with a commutative group $A$ contains a copy of $S$? Oct 2 comment When a semigroup extension $S \times A$ of a semigroup $S$ with a commutative group $A$ contains a copy of $S$? Thanks for comment, I replaced "semidirect product" with "semigroup extension". Oct 2 revised When a semigroup extension $S \times A$ of a semigroup $S$ with a commutative group $A$ contains a copy of $S$? changed "semidirect product" with "semigroup extension" Oct 2 asked When a semigroup extension $S \times A$ of a semigroup $S$ with a commutative group $A$ contains a copy of $S$? Sep 20 comment Computational complexity of multiplication in a nilpotent group? Thanks! Interesting that transformations of $A$ and $B$ into $3n \times 3n$ matrices are different! Sep 19 comment Computational complexity of multiplication in a nilpotent group? Dear Henry, after more thinking, I don't believe that "you can reduce n×n matrix multiplication to the 3n×3n upper triangular case. (Use nine n×n blocks, with identity matrices on the diagonal and a zero matrix in the upper right corner.)" There is something wrong there, are you saying that there is an injective morphism from $GL(n)$ to the group of $3n \times 3n$ upper triangular matrices? Sep 17 awarded Commentator Sep 15 comment Computational complexity of multiplication in a nilpotent group? You are right, I was hoping I missed something, that already for the Heisenberg group there is a difference. Sep 14 comment Computational complexity of multiplication in a nilpotent group? Actually, if anybody cares, here is explained the motivation for the question: chorasimilarity.wordpress.com/2012/09/14/… Sep 14 comment Computational complexity of multiplication in a nilpotent group? Thank you for the answer. What about the Heisenberg group $H(n) = R^{n} \times R^{n} \times R$? It has $m=2$. Sep 13 comment How fast can we *really* multiply matrices? Dear Henry, I asked a somehow related question, see mathoverflow.net/questions/106899/… Sep 12 revised Computational complexity of multiplication in a nilpotent group? added 1651 characters in body