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 DDcut_limit : forall (upcut : DedekindDecCut) (r : Q), Qlt 0 r -> { q : Q | DDupcut upcut q /\ ~DDupcut upcut (q - r) }.