A min-max relation for K3-covers in graphs noncontractible to K5e Original Research Article

In Euler and Mahjoub (1991) it is proved that the triangle-free subgraph polytope of a graph noncontractible to K5e is completely described by the trivial inequalities and the so-called triangle and odd wheel inequalities. In this paper we show that the system denned by those inequalities is TDI for a subclass of that class of graphs. As a consequence we obtain the following min-max relation: If G is a graph noncontractible to K5e, then the minimum number of edges covering all the triangles of G equals the maximum profit of a partition of the edge set of G into edges, triangles and odd wheels. Here the profit of an edge is 0, the profit of a triangle is 1 and the profit of a 2k + 1-wheel (k ϵ N) is equal to k + 1.