Admin/psbooklet

move lemma add_eq_0_iff to Groups.thy

#!/usr/bin/env bash
#
# 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)'