Fixpoint DDcut_limit_fix (upcut : DedekindDecCut) (r : Q) (n : nat) :
  Qlt 0 r
  -> (DDupcut upcut (DDlow upcut + (Z.of_nat n#1) * r))
  -> { q : Q | DDupcut upcut q /\ ~DDupcut upcut (q - r) }.

Lemma sig_lub : forall {R : ConstructiveReals} (E:CRcarrier R -> Prop), sig_forall_dec_T -> sig_not_dec_T -> (exists x : CRcarrier R, E x) -> (exists x : CRcarrier R, is_upper_bound E x) -> { u : CRcarrier R | is_lub E u }.