Infinite Graphic Matroids

02 Aug 2017

An infinite matroid is graphic if all of its finite minors are graphic and the intersection of any circuit with any cocircuit is finite. We show that a matroid is graphic if and only if it can be represented by a graph-like topological space: that is, a graph-like space in the sense of Thomassen and Vella. This extends Tutte’s characterization of finite graphic matroids. Working in the representing space, we prove that any circuit in a 3-connected graphic matroid is countable.