Removable Circuits in Multigraphs

We prove the following conjecture of Bill Jackson (J. London Math. Soc. (2)21, 1980, 391).If G is a2-connected multigraph with minimum degree at least4and containing no Petersen minor, then G contains a circuit C such that G−E(C) is2-connected. In fact,Ghas at leasttwoedge-disjoint circuits which can serve asC. Until now, the conjecture had been verified only for planar graphs and for simple graphs.