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math.CO2006
A proof of Bjorner's totally nonnegative conjecture
Michael Bjorklund, Alexander Engstrom
The McMullen Correspondence gives a linear dependence between M-sequences of length |d/2|+1 and f-vectors of simplical d-polytopes. Denote the transfer matrix between g and f by M_…
math.CO2005
Complexes of Directed Trees and Independence Complexes
Alexander Engstrom
The theory of complexes of directed trees was initiated by Kozlov to answer a question by Stanley, and later on, results from the theory were used by Babson and Kozlov in their pro…
math.CO2005
A short proof of a conjecture on the higher connectivity of graph coloring complexes
Alexander Engstrom
The Hom-complexes were introduced by Lovasz to study topological obstructions to graph colorings. It was conjectured by Babson and Kozlov, and proved by Cukic and Kozlov, that Hom(…
math.CO2005
Two multicolor Ramsey numbers
Alexander Engstrom
Two new bounds for multicolor Ramsey numbers are proved: and .