simp[ha]
α✝ : Type u
inst✝² : DecidableEq α✝
β✝ : Type v
inst✝¹ : DecidableEq β✝
m : Type u_3 → Type u_2
α : Type u_1
β : Type u_3
inst✝ : Monad m
f g : α → m β
a✝ : α
as : List α
ih : (∀ a ∈ as, f a = g a) → mapM' f as = mapM' g as
hf : ∀ a ∈ a✝ :: as, f a = g a
a : α
ha : a ∈ as
⊢ a ∈ a✝ :: as
no goals