A note on the production of matroid minors

Abstract

The circuits containing some fixed element of a connected matroid (such a collection is called a port) provide a matroid generalization of the “path collections” of graphs. In this note we show how to translate forbidden minor theorems in matroid theory into results about ports — and we find that many theorems are strengthened by such translation. Those collections of sets which are “path collections” of graphs may then be characterized.