--- a/src/HOL/Analysis/Sigma_Algebra.thy Sun Nov 11 12:13:24 2018 +0100
+++ b/src/HOL/Analysis/Sigma_Algebra.thy Sun Nov 11 14:34:02 2018 +0100
@@ -1333,7 +1333,7 @@
fix A assume "A \<subseteq> \<Omega> \<and> A \<inter> D \<in> M"
moreover have "(\<Omega> - A) \<inter> D = (\<Omega> - (A \<inter> D)) - (\<Omega> - D)"
by auto
- ultimately show "\<Omega> - A \<subseteq> \<Omega> \<and> (\<Omega> - A) \<inter> D \<in> M"
+ ultimately show "(\<Omega> - A) \<inter> D \<in> M"
using \<open>D \<in> M\<close> by (auto intro: diff)
next
fix A :: "nat \<Rightarrow> 'a set"
--- a/src/HOL/Set.thy Sun Nov 11 12:13:24 2018 +0100
+++ b/src/HOL/Set.thy Sun Nov 11 14:34:02 2018 +0100
@@ -1122,7 +1122,7 @@
text \<open>\<^medskip> Set difference.\<close>
-lemma Diff_subset: "A - B \<subseteq> A"
+lemma Diff_subset[simp]: "A - B \<subseteq> A"
by blast
lemma Diff_subset_conv: "A - B \<subseteq> C \<longleftrightarrow> A \<subseteq> B \<union> C"