∀ {α : Type u} {inst : LE α} {inst_1 : Std.PRange.UpwardEnumerable α} {inst_2 : Std.Rxc.HasSize α}
  [self : Std.Rxc.LawfulHasSize α] (lo hi lo' : α),
  lo ≤ hi → Std.PRange.succ? lo = some lo' → Std.Rxc.HasSize.size lo hi = Std.Rxc.HasSize.size lo' hi + 1