obsolete, cf. Proof_Context.print_syntax;
--- a/generic/proof-config.el 2008-07-21 18:37:10.000000000 +0200
+++ b/generic/proof-config.el 2009-11-29 17:41:37.409062091 +0100
@@ -1493,7 +1493,7 @@
:type '(choice string (const nil))
:group 'proof-shell)
-(defcustom proof-shell-quit-timeout 4
+(defcustom proof-shell-quit-timeout 45
;; FIXME could add option to quiz user before rude kill.
"The number of seconds to wait after sending proof-shell-quit-cmd.
After this timeout, the proof shell will be killed off more rudely.