∀ {ι : Type u_1} {κ : Type u_2} {M : Type u_4} [inst : CommMonoid M] [inst_1 : DecidableEq κ] (s : Finset ι)
  (t : Finset κ) (g : ι → κ) (f : κ → M), ∏ j ∈ t, ∏ i ∈ s with g i = j, f j = ∏ i ∈ s with g i ∈ t, f (g i)