diff -r 00bdc48c5f71 -r 1b01a57d2749 src/Doc/System/Sessions.thy
--- a/src/Doc/System/Sessions.thy	Sat Dec 15 12:55:11 2012 +0100
+++ b/src/Doc/System/Sessions.thy	Sat Dec 15 13:14:55 2012 +0100
@@ -348,16 +348,18 @@
   Options are:
     -L OPTION    default logic via system option
     -d DIR       include session directory
+    -l NAME      logic session name
     -s           system build mode: produce output in ISABELLE_HOME
 
-  Build Isabelle session image LOGIC via GUI dialog.
+  Build Isabelle logic session image via GUI dialog (default: \$ISABELLE_LOGIC).
 \end{ttbox}
 
-  \medskip Option @{verbatim "-L"} specifies a system option name as
-  fall-back, if the specified @{text "LOGIC"} name is empty.
+  \medskip Option @{verbatim "-l"} specifies an explicit logic session
+  name.  Option @{verbatim "-L"} specifies a system option name as
+  fall-back to determine the logic session name.  If both are omitted
+  or have empty value, @{setting ISABELLE_LOGIC} is used as default.
 
   \medskip Options @{verbatim "-d"} and @{verbatim "-s"} have the same
-  meaning as for the command-line @{tool build} tool itself.
-*}
+  meaning as for the command-line @{tool build} tool itself.  *}
 
 end