∀ {α : Type u} [inst : BEq α] [inst_1 : Hashable α] {m : Std.DHashMap.Raw α fun x => Unit} [EquivBEq α]
  [LawfulHashable α],
  m.WF →
    ∀ {l : List α},
      List.Pairwise (fun a b => (a == b) = false) l →
        (∀ a ∈ m, l.contains a = false) → (Std.DHashMap.Raw.Const.insertManyIfNewUnit m l).size = m.size + l.length