Embedded Graphs, Facial Colorings, and Double Cycle Covers
Paul A. Catlin · 1990
We use the notation of Bondy and Murty [4], except that graphs have no loops. Let H be a subgraph of G. The contraction G/H is the graph obtained from G by contracting all edges of H and deleting any resulting loops. Denote $$O(G)=\{odd-\deg ree\,vertices\,of\,G\}.$$