∀ {α : Type u} {β : α → Type v} [inst : BEq α] [inst_1 : Hashable α] {m₁ m₂ : Std.DHashMap.Raw α β}
  [inst_2 : LawfulBEq α], m₁.WF → m₂.WF → ∀ {k : α} [inst_3 : Inhabited (β k)], k ∉ m₂ → (m₁ \ m₂).get! k = m₁.get! k