Past exam of the mathematics course of the University of Cambridge 2022 iii Paper 204 1 b Solution 2026-09-28
Let be the uniform spanning tree measure on the finite connected induced graph . Uniform spanning-tree edge indicators are negatively associated: increasing events depending on disjoint edge sets have nonpositive covariance. Together with the spatial Markov property, this implies the free-boundary monotonicity under graph enlargement: for every increasing cylinder event , is eventually nonincreasing once contains all edges on which depends.
Define the free uniform spanning forest measure byfor increasing cylinder events. These limits determine a unique probability measure, independent of the exhaustion; equivalently, converges weakly to on the product space.