apply Finset.sum_congr rfl _
α : Type u_1
inst✝¹ : Fintype α
inst✝ : DecidableEq α
M : MultiPart α
x : ℕ
hx : x ∈ range (M.t + 1)
⊢ ∑ i in MultiPart.P M x, degree (mp M) i = ∑ x_1 in MultiPart.P M x, card (M.A \ MultiPart.P M x)
α : Type u_1
inst✝¹ : Fintype α
inst✝ : DecidableEq α
M : MultiPart α
x : ℕ
hx : x ∈ range (M.t + 1)
⊢ ∀ (x_1 : α), x_1 ∈ MultiPart.P M x → degree (mp M) x_1 = card (M.A \ MultiPart.P M x)