merged

--- a/src/HOL/Library/Multiset.thy	Mon Mar 22 17:33:08 2021 +0100
+++ b/src/HOL/Library/Multiset.thy	Mon Mar 22 21:24:25 2021 +0000
@@ -2333,7 +2333,7 @@
 
 end
 
-context ordered_cancel_comm_monoid_diff
+context cancel_comm_monoid_add
 begin
 
 lemma sum_mset_diff: