--- a/src/Pure/pure_thy.ML Sat Feb 24 17:21:35 2018 +0100
+++ b/src/Pure/pure_thy.ML Sun Feb 25 12:59:08 2018 +0100
@@ -105,6 +105,7 @@
("", typ "class_name => sort", Mixfix.mixfix "_"),
("_class_name", typ "id => class_name", Mixfix.mixfix "_"),
("_class_name", typ "longid => class_name", Mixfix.mixfix "_"),
+ ("_dummy_sort", typ "sort", Mixfix.mixfix "'_"),
("_topsort", typ "sort", Mixfix.mixfix "{}"),
("_sort", typ "classes => sort", Mixfix.mixfix "{_}"),
("", typ "class_name => classes", Mixfix.mixfix "_"),