∀ {α : Type u} {cmp : α → α → Ordering} {β : Type v} {t : Std.DTreeMap α (fun x => β) cmp} [inst : Std.TransCmp cmp]
  {a b : α} (hab : cmp a b = Ordering.eq) {h' : a ∈ t}, Std.DTreeMap.Const.get t a h' = Std.DTreeMap.Const.get t b ⋯