Added
goal Set.thy "(Union M = {}) = (! A : M. A = {})";
AddIffs [Union_empty_conv];
Good idea??
#!/bin/bash
#
# $Id$
#
# psbooklet - rearrange pages of ps file to be printed as booklet (duplex)
#
psbook "$@" | \
pstops '4:0L@.7(21cm,0cm)+1L@.7(21cm,14.85cm),3R@.7(0cm,14.85cm)+2R@.7(0cm,29.7cm)'