∀ {α : Type u} {β : Type v} {cmp : α → α → Ordering} [inst : Std.TransCmp cmp] {l : List (α × β)} {k k' fallback : 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 → (Std.ExtTreeMap.ofList l cmp).getKeyD k' fallback = k