“…In the special case of a hard-core self-repulsion and hard-core nearest-neighbor exclusion (i.e. no site can be multiply occupied and no pair of adjacent sites can be simultaneously occupied), the partition function of the lattice gas coincides with the independent-set polynomial in combinatorics (also known as the independence polynomial or the stable-set polynomial) [4,41,42,56,51,52,53,63,27,28,64,77,35]. Moreover, the hard-core lattice gas is the universal statistical-mechanical model in the sense that any statistical-mechanical model living on a vertex set V 0 can be mapped onto a gas of nonoverlapping "polymers" on V 0 , i.e.…”