congr
α : Type u_1
G : SimpleGraph α
inst✝² : Fintype α
inst✝¹ : DecidableEq α
inst✝ : DecidableRel G.Adj
B A : Finset α
hB : B ⊆ A
this : A \ (A \ B) = B
⊢ (∑ y in A \ B, ∑ x in B, if Adj G x y then 1 else 0) = ∑ v in A \ B, ∑ w in B, if Adj G v w then 1 else 0
case e_f
α : Type u_1
G : SimpleGraph α
inst✝² : Fintype α
inst✝¹ : DecidableEq α
inst✝ : DecidableRel G.Adj
B A : Finset α
hB : B ⊆ A
this : A \ (A \ B) = B
⊢ (fun y => ∑ x in B, if Adj G x y then 1 else 0) = fun v => ∑ w in B, if Adj G v w then 1 else 0