Tara Brough
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 Jan 16 awarded Scholar Jan 16 accepted Status of an open problem about semilinear sets Jan 16 comment Status of an open problem about semilinear sets Thanks very much, this is exactly the sort of thing I was looking for. This not only confirms that the problem is (at least as far as the authors of the paper are aware) still open, but gives a potential alternative approach to determining whether or not it is decidable. Jan 2 comment Status of an open problem about semilinear sets Thanks, I haven't had time to look at it in detail yet, but since it doesn't seem to say anything about stratification, I'm not sure how helpful it will be. Jul 4 awarded Yearling Oct 2 awarded Nice Question Jun 15 comment An extension of Lagrange's theorem to semigroups? (I was typing that comment quite slowly, so didn't see the two preceding comments until afterwards.) Jun 15 comment An extension of Lagrange's theorem to semigroups? That's a good example. It's already clear from considering finite monogenic semigroups that the order of a subsemigroup of a 'Smarandache Semigroup' doesn't have to divide the order of the semigroup, but this example shows that nothing I would call an 'analogue of Lagrange's theorem' holds. Jun 10 comment A semigroup with the property that $x^n = a$ has at least one solution Is $n$ a constant? Jun 8 comment Certain type of regular languages @Dylan: Thanks for fixing it! I think I used to know about that, but I haven't written anything on mathoverflow for a long time, so I forgot. Jun 7 comment Certain type of regular languages Sorry about the LaTeX failure in the second line. I don't know what that's about. Jun 7 answered Certain type of regular languages Mar 25 awarded Enthusiast Mar 19 comment Question about $\omega$-regular languages If I could see the specific example you are looking at, I might have more to say. In complete generality I could only suggest the approach I would probably take. (I don't know much about $\omega$-regular languages, but in general I prefer working with automata to other representations of languages.) Mar 17 comment Question about $\omega$-regular languages I think it's easy, given a Büchi automaton, to describe the finite prefixes of words accepted by the automaton. So perhaps you could first find a Büchi automaton accepting your language? (I think it's straightforward to do that from the $\omega$-regular expression.) Mar 2 comment Mapping from a finite index subgroup onto the whole group @Ben: Ah yes, of course! Thanks. Mar 2 comment Mapping from a finite index subgroup onto the whole group Nice! Do you happen to know of an example if we remove the requirement that $H$ has finite index in $G$? I rather expect it's possible then, but I haven't thought of an example yet. Mar 2 comment Mapping from a finite index subgroup onto the whole group Hi Victor. I knew I must be missing something, but I can't believe it was something so obvious! I should have checked what you wrote more thoroughly. Anyway, I deleted my answer, since it contributes nothing and so it's better for the question to still have 0 answers. Feb 27 comment Non-isomorphic groups with the same oriented Cayley graph Oh, you're right, sorry! I guess I thought you meant they were the only choices because you said 'the resulting Cayley graph is going to be...', which looked as if you were saying it would always be of that form. (By the way, I don't agree that there is 'not much choice' of 'mag' generating set for your $H$, or that it has to be symmetric. Consider $S = \{a,ab\}$ for example, where $a$ and $b$ are the generators of the factors.) Feb 27 comment Non-isomorphic groups with the same oriented Cayley graph Yes, it is for undirected graphs.