contradiction
case cons.h_2
α✝¹ : Type u_1
α✝ : Type u_2
f : α✝¹ → Option α✝
x y : α✝¹
ys : List α✝¹
ih : List.filterMap f ys = [] → x ∈ ys → f x = none
hx : x ∈ y :: ys
x✝ : Option α✝
b✝ : α✝
heq✝ : f y = some b✝
h : b✝ :: List.filterMap f ys = []
⊢ f x = none
no goals