diff -r df1b56b0d2a2 -r c4acd312bd53 src/Tools/isac/ROOT
--- a/src/Tools/isac/ROOT	Mon Dec 30 11:16:00 2019 +0100
+++ b/src/Tools/isac/ROOT	Wed Jan 15 11:47:38 2020 +0100
@@ -2,8 +2,6 @@
     Author: Walther Neuper, TU Graz, 130715
    (c) due to copyright terms
 
-$ export ISABELLE_VERSION=2018 # for libisabelle
-
 see ~~/etc/settings
   ISABELLE_BROWSER_INFO="$ISABELLE_HOME_USER/browser_info"
 before out-outcommenting (*, browser_info = true*) below and ...
@@ -26,3 +24,12 @@
   options [document = false (*, browser_info = true*)]
   theories
     Build_Isac
+
+(* run "./bin/isabelle build -v -b Lucas_Interpreter" *)
+session Lucas_Interpreter = HOL +
+  description \<open>
+    Session Isac restricted to code required for Lucas_Interpreter.
+  \<close>
+  options [document = false (*, browser_info = true*)]
+  theories
+    "Interpret/Interpret"