The main goal of this paper is to answer question 1.10 and
settle conjecture 1.11 of Benjamini-Lyons-Schramm [BLS99: ``Percolation
perturbations in potential theory and random walks''] relating harmonic
Dirichlet functions on a graph to those on the infinite clusters in the
uniqueness phase of Bernoulli percolation. We extend the result to more
general invariant percolations, including the Random-Cluster model. We
prove the existence of the nonuniqueness phase for the Bernoulli percolation
(and make some progress for Random-Cluster model) on unimodular transitive
locally finite graphs admitting nonconstant harmonic Dirichlet functions.
This is done by using the device of l2 Betti numbers.