intro; generalize (rho_ub_t_PI2 V t); intro; unfold rho_V in |- *...
apply Rlt_trans with (rho_ub V * t)%R...
apply Rmult_lt_compat_r...
apply Rlt_le_trans with MinT; [ apply MinT_is_pos | apply (cond_1 t) ]...
apply rho_ub_0...
Qed.

(**********)
Lemma rho_t_2 : forall t : TimeT, (rho_V * t < 2)%R.
Proof with trivial.