∀ {α : Type u} {instOrd : Ord α} {t : Std.DTreeMap.Internal.Impl α fun x => Unit} [Std.TransOrd α] [inst : BEq α]
  [Std.LawfulBEqOrd α] (h : t.WF) {l : List α} {k : α},
  Std.DTreeMap.Internal.Impl.Const.get? (↑(Std.DTreeMap.Internal.Impl.Const.insertManyIfNewUnit t l ⋯)) k =
    if k ∈ t ∨ l.contains k = true then some () else none