  Let G=(V,E) be a graph. Let k < |V| be an integer. Let O_k be the number of
edge induced subgraphs of G having k vertices and an odd number of edges. Let
E_k be the number of edge induced subgraphs of G having k vertices and an even
number of edges. Let D_k = O_k - E_k. The ODD EVEN DELTA problem consists in
computing D_k, given G and k. We show that such problem is #P-hard, even on
3-regular bipartite planar graphs.
