∀ {α : Type u} {cmp : α → α → Ordering} {β : Type v} {t : Std.DTreeMap α (fun x => β) cmp} [inst : Std.TransCmp cmp]
  {a : α} {h : (Std.DTreeMap.Const.get? t a).isSome = true},
  (Std.DTreeMap.Const.get? t a).get h = Std.DTreeMap.Const.get t a ⋯