diff -r 38e225bd53e4 -r a125b8040ada doc-src/System/Thy/Sessions.thy
--- a/doc-src/System/Thy/Sessions.thy	Sat Jul 28 22:01:21 2012 +0200
+++ b/doc-src/System/Thy/Sessions.thy	Sun Jul 29 21:40:46 2012 +0200
@@ -168,6 +168,7 @@
     -a           select all sessions
     -b           build heap images
     -d DIR       include session directory with ROOT file
+    -f           fresh build
     -g NAME      select session group NAME
     -j INT       maximum number of parallel jobs (default 1)
     -n           no build -- test dependencies only
@@ -221,6 +222,9 @@
   saved for inner nodes of the hierarchy of sessions, as required for
   other sessions to continue later on.
 
+  \medskip Option @{verbatim "-f"} ensures a fresh build, even if all
+  results are up-to-date wrt.\ the current set of sources.
+
   \medskip Option @{verbatim "-j"} specifies the maximum number of
   parallel build jobs (prover processes).  Note that each process is
   subject to a separate limit of parallel threads, cf.\ system option