--- a/src/HOL/Library/Multiset.thy Sat Sep 22 16:03:31 2018 +0200
+++ b/src/HOL/Library/Multiset.thy Sun Sep 23 12:50:12 2018 +0200
@@ -2385,7 +2385,7 @@
shows \<open>(\<Sum>x\<in>#A. y) = of_nat (size A) * y\<close>
by (induction A) (auto simp: algebra_simps)
-abbreviation Union_mset :: "'a multiset multiset \<Rightarrow> 'a multiset" ("\<Union># _" [900] 900)
+abbreviation Union_mset :: "'a multiset multiset \<Rightarrow> 'a multiset" ("\<Union>#")
where "\<Union># MM \<equiv> sum_mset MM" \<comment> \<open>FIXME ambiguous notation --
could likewise refer to \<open>\<Squnion>#\<close>\<close>