∀ {α : Type u} [inst : BEq α] [inst_1 : Hashable α] {β : Type v} {m₁ m₂ : Std.DHashMap.Internal.Raw₀ α fun x => β}
  [EquivBEq α] [LawfulHashable α],
  (↑m₁).WF →
    (↑m₂).WF →
      ∀ {k : α} {fallback : β},
        m₂.contains k = true → Std.DHashMap.Internal.Raw₀.Const.getD (m₁.diff m₂) k fallback = fallback