proposition: Lemma r_V_is_pos : (0 < r_V)%R.
proof: Proof. unfold r_V in |- *; unfold r in |- *; unfold Rdiv in |- *; apply Rmult_lt_0_compat; [ apply (TypeSpeed_pos V) | apply Rinv_0_lt_compat; apply rho_pos ]. Qed.
imports: Reals trajectory_const rrho trajectory_def