rattac.
unfold natToPosnat in *.
inversion H0; clear H0; subst.
repeat rewrite mult_1_r.
inversion H; clear H; subst.
trivial.
Qed.

(* Specifications: *)
Theorem ratDistance_comm : forall r1 r2,
eqRat (ratDistance r1 r2) (ratDistance r2 r1).