Representing polynomial of ST-CONNECTIVITY

We show that the coefficients of the representing polynomial of any monotone Boolean function are the values of a M\"obius function of an atomistic lattice related to this function. Using this we determine the representing polynomial of any Boolean function corresponding to a ST-CONNECTIVITY problem in acyclic quivers (directed acyclic multigraphs). Only monomials corresponding to unions of paths have non-zero coefficients which are $(-1)^D$ where $D$ is an easily computable function of the quiver corresponding to the monomial (it is the number of plane regions in the case of planar graphs). We estimate the number of monomials with non-zero coefficients for the two-dimensional grid connectivity problem as being between $\Omega(1.641^{2n^2})$ and $O(1.654^{2n^2})$.