Two Posets of Noncrossing Partitions Coming From Undesired Parking Spaces

Abstract

Consider the noncrossing set partitions of an n-element set which either do not contain the block {n − 1, n}, or which do not contain the singleton block {n} whenever 1 and n − 1 are in the same block. In this article we study the subposet of the noncrossing partition lattice induced by these elements, and show that it is a supersolvable lattice, and therefore lexicographically shellable. We give a combinatorial model for the NBB bases of this lattice and derive an explicit formula for the value of its Möbius function between least and greatest element. This work is motivated by a recent article by M. Bruce, M. Dougherty, M. Hlavacek, R. Kudo, and I. Nicolas, in which they introduce a subposet of the noncrossing partition lattice that is determined by parking functions with certain forbidden entries. In particular, they conjecture that the resulting poset always has a contractible order complex. We prove this conjecture by embedding their poset into ours, and showing that it inherits the lexicographic shellability.2010 Mathematics Subject Classification. 05A18, 06A07.

The Noncrossing Bond Poset of a Graph

“…More recently, motivated by the connection between the noncrossing partition lattice and parking functions, Bruce, Dougherty, Hlavacek, Kudo, and Nicolas [12] introduced a subposet of the noncrossing partition lattice obtained by removing chains that corresponded to parking functions with certain restrictions. To solve a conjecture put forward in that article, Mühle [23] defined two new subposets of the noncrossing partition lattice obtained by removing partitions which do not contain certain blocks. Mühle [23] showed that these new posets are graded, shellable, and supersolvable.…”

“…To solve a conjecture put forward in that article, Mühle [23] defined two new subposets of the noncrossing partition lattice obtained by removing partitions which do not contain certain blocks. Mühle [23] showed that these new posets are graded, shellable, and supersolvable.…”