A control arrangement for rail traffic in which a track is divided into sections or blocks upon which a train may not enter until the preceding train has left.
His topics include oriented matroids, the pattern recognition problem, and tope committees; Dehn-Sommerville type relations; blocking sets of set families, and absolute blocking constructions in posets; halfspaces, convex sets, and tope committees; tope committees containing no pairs of opposites; and symmetric cycles in the hypercube graphs.