Proof with trivial.
intros; unfold toDeg in |- *; repeat rewrite Rmult_assoc;
rewrite <- Ropp_mult_distr_l_reverse; rewrite (Rmult_comm (- MaxBank));
rewrite (Rmult_comm (phi tr t)); apply Rmult_le_compat_l...
left; apply Rmult_lt_0_compat...
unfold plat in |- *; prove_sup0...
apply Rinv_0_lt_compat; apply PI_RGT_0...
generalize (cond_phi tr); intro H; elim (H t)...
Qed.

Lemma cond2_sty :
forall (tr : Trajectory) (t : R), (toDeg (phi tr t) <= toDeg MaxBank)%R.