A Short Proof of Seymourʹs Characterization of the Matroids with the Max-Flow Min-Cut Property

Seymour proved that the set of odd circuits of a signed binary matroid (M,Σ) has the Max-Flow Min-Cut property if and only if it does not contain a minor isomorphic to (M(K4),E(K4)). We give a shorter proof of this result.