∀ {α : Type u} {β : α → Type v} {cmp : α → α → Ordering} [Std.TransCmp cmp] [inst : Std.LawfulEqCmp cmp]
  {l : List ((a : α) × β a)} {k k' : α} (k_eq : cmp k k' = Ordering.eq) {v : β k},
  List.Pairwise (fun a b => ¬cmp a.fst b.fst = Ordering.eq) l →
    ⟨k, v⟩ ∈ l → (Std.DTreeMap.ofList l cmp).get? k' = some (cast ⋯ v)