∀ {α : Type u} {β : Type v} {γ : Type w} {x : BEq α} {x_1 : Hashable α} {m : Std.HashMap α β} [EquivBEq α]
  [LawfulHashable α] [inst : Inhabited α] {f : α → β → γ} {k : α}, (Std.HashMap.map f m).getKey! k = m.getKey! k