diff -r a6ca869af096 -r b219774a71ae src/Pure/General/path.scala
--- a/src/Pure/General/path.scala	Wed Mar 31 21:44:29 2021 +0200
+++ b/src/Pure/General/path.scala	Wed Mar 31 22:10:56 2021 +0200
@@ -87,6 +87,9 @@
   def variable(s: String): Path = new Path(List(variable_elem(s)))
   val parent: Path = new Path(List(Parent))
 
+  val USER_HOME: Path = variable("USER_HOME")
+  val ISABELLE_HOME: Path = variable("ISABELLE_HOME")
+
 
   /* explode */