Let σ σ = { σ σ j } j ∈ ∈ Λ Λ be a configuration of (continuous or discrete) spins on a lattice Λ. If A ⊂ Λ is a list of lattice sites, possibly with duplicates, let σ σ A = ∏ ∏ j ∈ ∈ A σ σ j be the product of the spins in A.