∀ {α : Type u} {β : α → Type v} {instOrd : Ord α} {t : Std.DTreeMap.Internal.Impl α β} [Std.TransOrd α],
  t.WF →
    ∀ {l : List ((a : α) × β a)} {k k' : α},
      compare k k' = Ordering.eq →
        List.Pairwise (fun a b => ¬compare a.fst b.fst = Ordering.eq) l →
          k ∈ List.map Sigma.fst l → (↑(t.insertMany! l)).getKey? k' = some k