diff -r 898cac1dad5e -r 366c4a602500 lib/Tools/build_dialog
--- a/lib/Tools/build_dialog	Thu Dec 06 20:26:14 2012 +0100
+++ b/lib/Tools/build_dialog	Thu Dec 06 21:16:46 2012 +0100
@@ -15,7 +15,6 @@
   echo "Usage: isabelle $PRG [OPTIONS] LOGIC"
   echo
   echo "  Options are:"
-  echo "    -C           check for existing image"
   echo "    -L OPTION    default logic via system option"
   echo "    -d DIR       include session directory"
   echo "    -s           system build mode: produce output in ISABELLE_HOME"
@@ -34,17 +33,13 @@
 
 ## process command line
 
-CHECK_EXISTING=false
 LOGIC_OPTION=""
 declare -a INCLUDE_DIRS=()
 SYSTEM_MODE=false
 
-while getopts "CL:d:s" OPT
+while getopts "L:d:s" OPT
 do
   case "$OPT" in
-    C)
-      CHECK_EXISTING="true"
-      ;;
     L)
       LOGIC_OPTION="$OPTARG"
       ;;
@@ -75,5 +70,5 @@
 [ -e "$ISABELLE_HOME/Admin/build" ] && { "$ISABELLE_HOME/Admin/build" jars || exit $?; }
 
 "$ISABELLE_TOOL" java isabelle.Build_Dialog \
-  "$CHECK_EXISTING" "$LOGIC_OPTION" "$SYSTEM_MODE" "$LOGIC" "${INCLUDE_DIRS[@]}"
+  "$LOGIC_OPTION" "$SYSTEM_MODE" "$LOGIC" "${INCLUDE_DIRS[@]}"