A short proof of Tutte's characterization of totally unimodular matrices

AbstractWe give, in terms of totally unimodular matrices, a short and easy proof of Tutte's characterization of regular matroids

On shortest TT-joins and packing TT-cuts

We give a class of graphs with the property that for each even set T of nodes in G the minimum length of a T-join is equal to the maximum number of pairwise edge disjoint T-cuts. Our class contains the bipartite and the series-parallel graphs for which this property was derived earlier by Seymour

Excluding a group-labelled graph

This paper contains a first step towards extending the Graph Minors Project of Robertson and Seymour to group-labelled graphs. For a finite abelian group Γ and Γ-labelled graph G, we describe the class of Γ-labelled graphs that do not contain a minor isomorphic to G