∀ {α : Type u} {β : Type v} {cmp : α → α → Ordering} {t : Std.ExtTreeMap α β cmp} [inst : Std.TransCmp cmp]
  {l : List (α × β)} {k k' : α},
  cmp k k' = Ordering.eq →
    List.Pairwise (fun a b => ¬cmp a.1 b.1 = Ordering.eq) l →
      k ∈ List.map Prod.fst l → (t.insertMany l).getKey? k' = some k