∀ {α : Type u} {β : α → Type v} [inst : BEq α] [inst_1 : Hashable α] {m₁ m₂ : Std.DHashMap.Internal.Raw₀ α β}
  [EquivBEq α] [LawfulHashable α], (↑m₁).WF → (↑m₂).WF → (↑m₁).size ≤ (↑(m₁.union m₂)).size