Hypothesis (Hnb_steps : (1 < nb_steps)%Z).

Lemma inbetween_step_not_Eq :
forall x k l l',
inbetween (start + Z2R k * step) (start + Z2R (k + 1) * step) x l ->
(0 < k < nb_steps)%Z ->
Rcompare x (start + (Z2R nb_steps / 2 * step))%R = l' ->
inbetween start (start + Z2R nb_steps * step) x (loc_Inexact l').