Some Extremal Problems on Graphs and Partial Orders
Liu, Qi
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https://hdl.handle.net/2142/86887
Description
Title
Some Extremal Problems on Graphs and Partial Orders
Author(s)
Liu, Qi
Issue Date
2007
Doctoral Committee Chair(s)
West, Douglas B.
Department of Study
Mathematics
Discipline
Mathematics
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Mathematics
Language
eng
Abstract
A unichain in a product poset P x Q is a chain in which the value of one coordinate is fixed. A semiantichain in P x Q is a family S such that (u, v) < ( u', v') for two elements of S only if u < u' and v < v' . Saks and West conjectured that for every product of partial orders, the maximum size of a semiantichain equals the minimum number of unichains needed to cover the product. We prove the case where both factors have width 2. We also use the characterization of product graphs that are perfect to prove other special cases, including the case where both factors have height 2. Finally, we make an observation about the case where both factors have dimension 2.
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