diff -r a6ba77af6486 -r cef000855cf4 src/Pure/Thy/export_theory.scala
--- a/src/Pure/Thy/export_theory.scala	Wed Sep 19 22:18:36 2018 +0200
+++ b/src/Pure/Thy/export_theory.scala	Thu Sep 20 22:39:39 2018 +0200
@@ -328,12 +328,12 @@
   /* type classes */
 
   sealed case class Class(
-    entity: Entity, params: List[(String, Term.Typ)], axioms: List[Term.Term])
+    entity: Entity, params: List[(String, Term.Typ)], axioms: List[Prop])
   {
     def cache(cache: Term.Cache): Class =
       Class(entity.cache(cache),
         params.map({ case (name, typ) => (cache.string(name), cache.typ(typ)) }),
-        axioms.map(cache.term(_)))
+        axioms.map(_.cache(cache)))
   }
 
   def read_classes(provider: Export.Provider): List[Class] =
@@ -344,7 +344,7 @@
         {
           import XML.Decode._
           import Term_XML.Decode._
-          pair(list(pair(string, typ)), list(term))(body)
+          pair(list(pair(string, typ)), list(decode_prop))(body)
         }
         Class(entity, params, axioms)
       })
@@ -356,13 +356,13 @@
     entity: Entity,
     typargs: List[(String, Term.Sort)],
     args: List[(String, Term.Typ)],
-    axioms: List[Term.Term])
+    axioms: List[Prop])
   {
     def cache(cache: Term.Cache): Locale =
       Locale(entity.cache(cache),
         typargs.map({ case (name, sort) => (cache.string(name), cache.sort(sort)) }),
         args.map({ case (name, typ) => (cache.string(name), cache.typ(typ)) }),
-        axioms.map(cache.term(_)))
+        axioms.map(_.cache(cache)))
   }
 
   def read_locales(provider: Export.Provider): List[Locale] =
@@ -373,7 +373,7 @@
         {
           import XML.Decode._
           import Term_XML.Decode._
-          triple(list(pair(string, sort)), list(pair(string, typ)), list(term))(body)
+          triple(list(pair(string, sort)), list(pair(string, typ)), list(decode_prop))(body)
         }
         Locale(entity, typargs, args, axioms)
       })