∀ {α : Type u} {β : α → Type v} {x : BEq α} {x_1 : Hashable α} [inst : EquivBEq α] [inst_1 : LawfulHashable α]
  (f f_1 : (a : α) → β a → Bool),
  f = f_1 → ∀ (m m_1 : Std.ExtDHashMap α β), m = m_1 → Std.ExtDHashMap.filter f m = Std.ExtDHashMap.filter f_1 m_1