Order

, Volume 26, Issue 2, pp 101–107

The First Three Levels of an Order Preserving Hamiltonian Path in the Subset Lattice

Article

DOI: 10.1007/s11083-009-9107-y

Cite this article as:
Biró, C. & Howard, D.M. Order (2009) 26: 101. doi:10.1007/s11083-009-9107-y

Abstract

Consider the lattice whose elements are the subsets of the set of positive integers not greater than n ordered by inclusion. The Hasse diagram of this lattice is isomorphic to the n-dimensional hypercube. It is trivial that this graph is Hamiltonian. Let \(\{S_1,\ldots,S_{2^n}\}\) be a Hamiltonian path. We say it is monotone, if for every i, either (a) all subsets of Si appear among S1,...,Si − 1, or (b) only one (say S) does not, furthermore Si + 1 = S. Trotter conjectured that if n is sufficiently large, then there are no monotone Hamiltonian paths in the n-cube. He also made a stronger conjecture that states that there is no path with the monotone property that covers all the sets of size at most three. In this paper we disprove this strong conjecture by explicitly constructing a monotone path covering all the 3-sets.

Keywords

Hamiltonian path Boolean lattice Gray code 

Copyright information

© Springer Science+Business Media B.V. 2009

Authors and Affiliations

  1. 1.School of MathematicsGeorgia Institute of TechnologyAtlantaUSA

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