∀ {α : Type u} {β : Type v} {γ : Type w} {x : BEq α} {x_1 : Hashable α} {m : Std.ExtHashMap α β} [inst : EquivBEq α]
  [inst_1 : LawfulHashable α] [inst_2 : Inhabited α] {f : α → β → Option γ} {k : α},
  (Std.ExtHashMap.filterMap f m).getKey! k = ((m.getKey? k).pfilter fun x_2 h' => (f x_2 m[x_2]).isSome).get!