We study idealized random sequential adsorption on a lattice, with ads
orption probabilities inhomogeneous both in space and in time, and inc
luding the possibility of cooperativity. Attention is directed to the
mean occupancy of a given site as a function of time, which is represe
nted by a weighted random walk on the lattice. In the special case of
nearest neighbor exclusion, the walk is transformed to one in which on
ly neighbors of occupied sites can be occupied, but with a renormalize
d probability. Reduction theorems are presented, with which the genera
l case of a tree lattice is completely solved in inverse form.