∀ {α : Type u} {cmp : α → α → Ordering} {t : Std.ExtTreeSet α cmp} {δ : Type w} {m : Type w → Type w'}
  [inst : Std.TransCmp cmp] [inst_1 : Monad m] [inst_2 : LawfulMonad m] {f : δ → α → m δ} {init : δ},
  Std.ExtTreeSet.foldlM f init t = List.foldlM f init t.toList