Planar Lattices

Abstract

A finite partially ordered set (poset) P is customarily represented by drawing a small circle for each point, with a lower than b whenever a < b in P, and drawing a straight line segment from a to b whenever a is covered by b in P (see, for example, G. Birkhoff [ 2 , p. 4]). A poset P is planar if such a diagram can be drawn for P in which none of the straight line segments intersect.