left; apply Rinv_lt_contravar; auto.
apply Rmult_lt_0_compat; auto.
apply Rlt_trans with (2 := H2); auto.
rewrite H2; auto with real.
Qed.

(* Specifications: *)
Theorem Int_part_INR : forall n : nat, Int_part (INR n) = Z_of_nat n.
intros n; unfold Int_part in |- *.