TAILIEUCHUNG - Báo cáo toán học: "Cubical Convex Ear Decompositions"

Tuyển tập các báo cáo nghiên cứu khoa học ngành toán học tạp chí toán học quốc tế đề tài: Cubical Convex Ear Decompositions. | Cubical Convex Ear Decompositions Russ Woodroofe Department of Mathematics Washington University in St. Louis St. Louis MO 63130 USA russw@ Submitted Aug 8 2008 Accepted Jun 5 2009 Published Jun 10 2009 Mathematics Subject Classification 05E25 Dedicated to Anders Bjorner in honor of his 60th birthday. Abstract We consider the problem of constructing a convex ear decomposition for a poset. The usual technique introduced by Nyman and Swartz starts with a CL-labeling and uses this to shell the ears of the decomposition. We axiomatize the necessary conditions for this technique as a CL-ced or EL-ced . We find an EL-ced of the d-divisible partition lattice and a closely related convex ear decomposition of the coset lattice of a relatively complemented finite group. Along the way we construct new EL-labelings of both lattices. The convex ear decompositions so constructed are formed by face lattices of hypercubes. We then proceed to show that if two posets P1 and P2 have convex ear decompositions CL-ceds then their products P1 X P2 P1 X P2 and Pl X P2 also have convex ear decompositions CL-ceds . An interesting special case is if P1 and P2 have polytopal order complexes then so do their products. Contents 1 Introduction 2 2 Definitions and tools 3 Convex ear decompositions. 4 Shellings. 4 Supersolvable lattices. 5 Cohen-Macaulay complexes . 6 EL-ceds and CL-ceds. 7 THE ELECTRONIC JOURNAL OF COMBINATORICS 16 2 2009 R17 1 3 The d-divisible partition lattice 9 A dual EL-labeling for nn. 10 An EL-ced for nn. 13 4 The coset lattice 17 Group theory background . 17 A dual EL-labeling for C G . 18 A convex ear decomposition for C G . 20 5 Poset products 24 Poset products and polytopes. 24 Convex ear decompositions of product posets. 27 Product CL-labelings. 28 CL-ceds of product posets. 29 6 Further questions 30 1 Introduction Convex ear decompositions introduced by Chari in 6 break a simplicial complex into .

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