Abstract
A particular version of the lattice model of Abraham and Heilmann (1972) for hydrogen-bonded systems is worked out by means of a weak subgraph expansion. Each site may be occupied by one molecule, A or B, and two neighbouring molecules. A may bind together, as far as neither of them is already engaged in more than one bond. It turns out that, for a wide range of the parameters involved in the model, the zeroth approximation (replacement of the true lattice by a Bethe lattice) leads to reasonable values of its thermodynamic properties.