An analogue of distributivity for ungraded lattices
Abstract
Description
In this paper, we define a property, trimness, for lattices. Trimness is a not-necessarily-graded generalization of distributivity; in particular, if a lattice is trim and graded, it is distributive. Trimness is preserved under taking intervals and suitable sublattices. Trim lattices satisfy a weakened form of modularity. The order complex of a trim lattice is contractible or homotopic to a sphere; the latter holds exactly if the maximum element of the lattice is a join of atoms.
Other than distributive lattices, the main examples of trim lattices are the Tamari lattices and various generalizations of them. We show that the Cambrian lattices in types A and B defined by Reading are trim, and we conjecture that all Cambrian lattices are trim.
19 pages, 4 figures. Version 2 includes small improvements to exposition, corrections of typos, and a new section showing that if a group G acts on a trim lattice by lattice automorphisms, then the sublattice of L consisting of elements fixed by G is trim
19 pages, 4 figures. Version 2 includes small improvements to exposition, corrections of typos, and a new section showing that if a group G acts on a trim lattice by lattice automorphisms, then the sublattice of L consisting of elements fixed by G is trim