1.1 --- a/src/HOL/Set.thy	Wed May 26 19:06:09 2004 +0200
     1.2 +++ b/src/HOL/Set.thy	Fri May 28 11:19:15 2004 +0200
     1.3 @@ -1108,6 +1108,9 @@
     1.4  lemma Collect_disj_eq: "{x. P x | Q x} = {x. P x} \<union> {x. Q x}"
     1.5    by blast
     1.6  
     1.7 +lemma Collect_imp_eq: "{x. P x --> Q x} = -{x. P x} \<union> {x. Q x}"
     1.8 +  by blast
     1.9 +
    1.10  lemma Collect_conj_eq: "{x. P x & Q x} = {x. P x} \<inter> {x. Q x}"
    1.11    by blast
    1.12