Remark return_measure_rec_incr:
forall f n1 n2 pc,
(n1 <= n2)%nat ->
(return_measure_rec n1 f pc <= return_measure_rec n2 f pc)%nat.

Lemma is_return_measure_rec:
forall f n n' pc r,
is_return n f pc r = true -> (n <= n')%nat ->
return_measure_rec n f.(fn_code) pc = return_measure_rec n' f.(fn_code) pc.