fixed an escaping error, added more infos to the generic error, callback catches...

[helm.git] / matita / dama / groups.ma

diff --git a/matita/dama/groups.ma b/matita/dama/groups.ma
index 1b39c1518348e7431de23d10ee1d2e6fc3dcf86f..699bd73fc3286190a3dbcf9ee3c643b0d8b9ce38 100644 (file)
--- a/matita/dama/groups.ma
+++ b/matita/dama/groups.ma
@@ -126,4 +126,15 @@ theorem eq_opp_opp_x_x: ∀G:abelian_group.∀x:G.--x=x.
  rewrite > plus_comm;
  rewrite > opp_inverse;
  reflexivity.
+qed.
+
+theorem eq_zero_opp_zero: ∀G:abelian_group.0=-0.
+ [ assumption
+ | intros;
+   apply (cancellationlaw ? 0);
+   rewrite < plus_comm in ⊢ (? ? ? %);
+   rewrite > opp_inverse;
+   rewrite > zero_neutral;
+   reflexivity
+ ].
 qed.
\ No newline at end of file