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Results tagged with co.combinatorics
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user 54838
Enumerative combinatorics, graph theory, order theory, posets, matroids, designs and other discrete structures. It also includes algebraic, analytic and probabilistic combinatorics.
5
votes
1
answer
212
views
Reconstructing an oriented matroid from its deletion and contraction
Suppose that $\mathcal{M}_1$ and $\mathcal M_2$ are two oriented matroids on the same ground set $E$. Under what conditions on $\mathcal{M}_1$ and $\mathcal{M}_2$ is there an oriented matroid $\mathca …
- 436
4
votes
Tableaux with limited rows and complementary skew shapes
Here is another solution, based on the paper "Robinson-schensted algorithms for skew tableaux" by Sagan and Stanley (Darij Grinberg was the one who suggested that this algorithm might work, I'm just f …
- 436
4
votes
Accepted
Schur positivity on 2 letter alphabets implies Schur-positivity on n letters?
My intuition is that if $P$ is in three variables then your requirements only force $P$ to be unimodal in each pair of variables, while being Schur positive is much more restrictive. For example, take …
- 436
3
votes
Accepted
Reconstructing an oriented matroid from its deletion and contraction
Found the answer in a paper by Ziegler & Richter-Gebert, see Theorem 4.1. Basically, they show that if two oriented matroids $\mathcal{M}_1$, $\mathcal{M}_2$ of ranks $r$ and $r-1$ respectively satis …
- 436