 Besides questions of optimizing transport and routing, the same techniques are fitted to the problem of minimal covering, some combinatorial teasers, problems in set theory, and linear programming.The methods continue to solve problems in some subsequent chapters; in one on couplages we find a problem typical of the applied scope of this theory.In what are called simple graphs, the vertices are divided into two sets such that all arcs connect only members of one set with points of the other.