Description of closure operators in convex geometries of segments on a line

Abstract

Convex geometry is a closure space $(G,\varphi )$ with the anti-exchange property. A classical result of Edelman and Jamison (1985) claims that every finite convex geometry is a join of several linear sub-geometries, and the smallest number of such sub-geometries necessary for representation is called the convex dimension. In our work we find necessary and sufficient conditions on a closure operator $\varphi$ of convex geometry $(G,\varphi )$ so that its convex dimension equals 2, equivalently, they are represented by segments on a line. These conditions can be checked in polynomial time in two parameters: the size of the base set $|G|$ and the size of the implicational basis of $(G,\varphi )$.

18 pages, 5 figures