rw [nbhdRes_filter,sum_filter]
case e_f.h
α : Type u_1
G : SimpleGraph α
inst✝² : Fintype α
inst✝¹ : DecidableEq α
inst✝ : DecidableRel G.Adj
B A : Finset α
x : α
⊢ ∑ x in nbhdRes G x A, 1 = ∑ w in A, if Adj G x w then 1 else 0
no goals