∀ {α : Type u} {β : Type v} {γ : Type w} {x : BEq α} {x_1 : Hashable α} [inst : EquivBEq α] [inst_1 : LawfulHashable α]
  (f f_1 : α → β → γ),
  f = f_1 → ∀ (m m_1 : Std.ExtHashMap α β), m = m_1 → Std.ExtHashMap.map f m = Std.ExtHashMap.map f_1 m_1