Let G = ( V , E ) be a graph, and ω ω : E → → { 0 , 1 } be a bond configuration on the graph that maps each edge to a value of either 0 or 1. We say that a bond is closed on edge e ∈ ∈ E if ω ω ( e ) = 0 , and open if ω ω ( e ) = 1 . If we let A ( ω ω ) = { e ∈ ∈ E : ω ω ( e ) = 1 } be the set of open bonds, then an open cluster or FK cluster is any connected component in A ( ω ω ) union the set of vertices. Note that an open cluster can be a single vertex (if that vertex is not incident to any open bonds).