intros n m H'; try assumption.
replace n with (m + (n - m)).
rewrite minus_plus.
apply
Trans
with
(sgroup_law G (sgroup_law G (nat_to_group m) (nat_to_group (n - m)))
(group_inverse G (nat_to_group m))); auto with *.
apply GROUP_reg_right with (nat_to_group m); auto with *.
apply
Trans
with
(sgroup_law G (sgroup_law G (nat_to_group m) (nat_to_group (n - m)))
(sgroup_law G (group_inverse G (nat_to_group m)) (nat_to_group m)));
auto with *.
apply
Trans
with
(sgroup_law G (sgroup_law G (nat_to_group m) (nat_to_group (n - m)))
(monoid_unit G)); auto with *.
apply Trans with (sgroup_law G (nat_to_group m) (nat_to_group (n - m)));
auto with *.
auto with *.
Qed.
Hint Resolve nat_to_group_minus: algebra.

(* Specifications: *)
Lemma ax8 :
forall p q : positive,
Pcompare p q Datatypes.Eq = Datatypes.Lt ->
Pcompare q p Datatypes.Eq = Datatypes.Gt.