The freeness Index of a graph

Abstract

We define a new integer invariant of a finite graph G, the freeness index, that measures the extent to which G can be embedded in the 3-sphere so that it and its subgraphs have ``simple" complements, i.e., complements which are homeomorphic to a connect-sum of handlebodies. We relate the freeness index to questions of embedding graphs into surfaces, in particular to the orientable cycle double cover conjecture. We show that a cubic graph satisfying the orientable double cycle cover conjecture has freeness index at least two.