--- a/QuotScript.thy Fri Oct 16 16:51:01 2009 +0200
+++ b/QuotScript.thy Fri Oct 16 17:05:52 2009 +0200
@@ -307,8 +307,14 @@
assumes q: "QUOTIENT R Abs Rep"
and a: "R x1 x2"
shows "R x1 (Rep (Abs x2))"
-using a
-by (metis QUOTIENT_REL[OF q] QUOTIENT_ABS_REP[OF q] QUOTIENT_REP_REFL[OF q])
+ and "R (Rep (Abs x1)) x2"
+proof -
+ show "R x1 (Rep (Abs x2))"
+ using q a by (metis QUOTIENT_REL[OF q] QUOTIENT_ABS_REP[OF q] QUOTIENT_REP_REFL[OF q])
+next
+ show "R (Rep (Abs x1)) x2"
+ using q a by (metis QUOTIENT_REL[OF q] QUOTIENT_ABS_REP[OF q] QUOTIENT_REP_REFL[OF q] QUOTIENT_SYM[of q])
+qed
(* ----------------------------------------------------- *)
(* Quantifiers: FORALL, EXISTS, EXISTS_UNIQUE, *)