∀ {α : Type u} {x : BEq α} {x_1 : Hashable α} {β : α → Type v} {m₁ m₂ : Std.ExtDHashMap α β} [inst : EquivBEq α]
  [inst_1 : LawfulHashable α] {k : α}, (m₁ ∩ m₂).contains k = (m₁.contains k && m₂.contains k)