We present the smallest non-lattice orthomodular poset and show that it is unique up to isomorphism. Since not every Boolean orthomodular, we consider class of skew posets previously introduced by first third author under name “generalized posets”. this contains all study its subclass consisting horizontal sums posets. For purpose, introduce concept a compatibility relation so-called commutator...

The poset retraction problem for a poset P is whether a given poset Q containing P as a subposet admits a retraction onto P, that is, whether there is a homomorphism from Q onto P which fixes every element of P. We study this problem for finite series-parallel posets P. We present equivalent combinatorial, algebraic, and topological charaterisations of posets for which the problem is tractable,...

On-line chain partitioning problem of on-line posets has been open for the past 20 years. The best known on-line algorithm uses 5 w −1 4 chains to cover poset of width w. Felsner [3] introduced a variant of this problem considering only up-growing posets, i.e. on-line posets in which each new point is maximal at the moment of its arrival. He presented an algorithm using (

We prove a theorem allowing us to find convex-ear decompositions for rankselected subposets of posets that are unions of Boolean sublattices in a coherent fashion. We then apply this theorem to geometric lattices and face posets of shellable complexes, obtaining new inequalities for their h-vectors. Finally, we use the latter decomposition to give a new interpretation to inequalities satisfied ...

We show that every comparability graph of any two-dimensional poset over n elements (a.k.a. permutation graph) can be preprocessed in O(n) time, if two linear extensions of the poset are given, to produce an O(n) space data-structure supporting distance queries in constant time. The data-structure is localized and given as a distance labeling, that is each vertex receives a label of O(log n) bi...

We prove that if a nite lattice L has order dimension at most d, then the homology of the order complex of its proper part L vanishes in dimensions d ? 1 and higher. In case L can be embedded as a join-sublattice in N d then L actually has the homotopy type of a simplicial complex with d vertices. 1. Introduction. The order dimension OrderDim(P) of a nite partially ordered set (poset for short)...

We study differential posets, a family of partially ordered sets discovered by Richard Stanley. In the first half of this paper we present an introduction to poset theory as relevant to differential posets and theorems on the structure and combinatorial properties of differential posets, culminating in the explicit definition of a new differential poset. In the second half we focus on Young’s l...