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35 Shellability

Input: Finite abstract pure simplicial complex Δ given by a list of facets
Output: "Yes" if Δ is shellable, "No" otherwise
Status (general): Open
Status (fixed dim.): Open
Given an ordering of the facets of Δ, it can be tested in polynomial time whether it is a shelling order. Hence, the problem in NP.

The problem can be solved in polynomial time for one-dimensional complexes, i.e., for graphs: a graph is shellable if and only if it is connected. Even for dim(Δ) = 2, the status is open. In particular, it is unclear if the problem can be solved in polynomial time if Δ is given by a list of all simplices.

For two-dimensional pseudo-manifolds the problem can be solved in linear time (Danarj and Klee [13]).


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