NEWS

   - Introduced alternative characterizations of the multiset ordering in
     "Library/Multiset_Order".
   - Renamed
       in_multiset_of ~> in_multiset_in_set
     INCOMPATIBILITY.
+  - Removed mcard, is equal to size.
   - Added attributes:
       image_mset.id [simp]
       image_mset_id [simp]
       elem_multiset_of_set [simp, intro]
       comp_fun_commute_plus_mset [simp]