A PROOF of Weak Graph Positivity, for a Large Range of the Parameters

One deals with r-regular bipartite graphs with 2n vertices. In a previous paper Butera, Pernici, and the author have introduced a quantity d(i), a function of the number of i-matchings, and conjectured that as n goes to infinity the fraction of graphs that satisfy Delta^k( d(i)) is non-negative, for all k and i, approaches 1. Here Delta is the finite difference operator. This conjecture we called the "graph positivity conjecture". "Weak graph positivity" is the conjecture that for each i and k the probability that Delta^k (d(i) is non-negative goes to 1 as n goes to infinity. Here we prove this for the range of parameters where r < 11, i+k < 101, k < 21, or i+k < 30 all r. A formalism of Wanless as systematized by Pernici is central to this effort.

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