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Apr
6
comment Missing citations of “to appear” papers on MathSciNet
The "to appear" articles usually don't have a MathSciNet entry associated with them yet. I read the linked webpage as saying that having e.g. an MR number assigned as being the deciding factor as to whether or not the citation is assigned correctly.
Apr
6
answered Missing citations of “to appear” papers on MathSciNet
Apr
4
comment Positivity of the alternating sum of indices for boolean interval of finite groups
You might look at (4.1.1) of "Poset topology: tools and applications", by Michelle Wachs. That survey paper also explains why this holds. It is possible for a Cohen-Macaulay poset to have 0 as its Möbius number, for example if it is contractible. That's maybe another reason to use the EL-labeling machinery -- that gives you an explicit calculation for the Möbius number as the number of decreasing chains. See Theorem 3.2.4 of the same survey paper.
Apr
4
comment Positivity of the alternating sum of indices for boolean interval of finite groups
The main point is that the Möbius number of a poset is an Euler characteristic of the associated order complex. See en.wikipedia.org/wiki/Poset_topology .
Apr
4
comment Positivity of the alternating sum of indices for boolean interval of finite groups
There are lots of ways to prove a complex to be Cohen-Macaulay. Actually, you only need for the order complex to have the homology of a bouquet of spheres in a fixed dimension with the right parity. I edited the post for clarity.
Apr
4
revised Positivity of the alternating sum of indices for boolean interval of finite groups
edited for clarity, following comment/question of original author
Apr
3
awarded  Revival
Apr
2
answered Positivity of the alternating sum of indices for boolean interval of finite groups
Apr
1
answered Generating finite simple groups with $2$ elements
Feb
15
comment List of counting proofs instead of linear algebra method in combinatorics
Is it possible that there might be some kind of shifting-type proof of Oddtown?
Jan
15
awarded  Nice Answer
Jan
4
comment Generalization of $(HK:H)=(K:H\cap K)$
As you might have already noticed, you don't need $H$ to normalize $K$ for (*) to hold, only for the two groups to permute setwise.
Dec
8
answered f vectors of simplicial complexes homeomorphic to n dimensional spheres
Dec
4
awarded  Yearling
Jul
14
awarded  Necromancer
Jul
13
awarded  Revival
Jul
13
comment Generating random finite groups
It's not clear to me that the procedure described above wouldn't favor certain isomorphism classes. The original question wanted an equal chance at each isomorphism class of groups of order $n$.
Jul
13
comment Generating random finite groups
Indeed, GAP even knows the count of these groups with NumberSmallGroups (but it won't let you get at the groups themselves via the SmallGroups library).
Jul
13
answered Generating random finite groups
May
15
answered Is there a (satisfying) proof that cellular cohomology is isomorphic to simplicial cohomology that doesn't use relative cohomlogy?