Discrete CATS Seminar
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UNIVERSITY OF KENTUCKY **

DISCRETE CATS SEMINAR

DISCRETE MATH AND COMBINATORICS: ALGEBRAIC & TOPOLOGICAL SEMINAR

113 PATTERSON OFFICE TOWER

FALL 2007

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"Restricted lattice paths and the cd-index of a product"

Michael Slone

University of Kentucky

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Monday, November 12, 2007

4:00 pm, 113 Patterson Office Tower

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Abstract:

A butterfly poset is the face poset of a regular subdivision of a
sphere with two cells in each dimension. The cd-index of a diamond
product of such posets has coefficients which can be interpreted as
counting lattice paths satisfying a certain restriction. We show how
this interpretation arises naturally from the coalgebraic point of
view. We will also prove a unimodality result on the coefficients of
such a product with fixed total rank. This reports on joint work with
Richard Ehrenborg.