#!/usr/local/plan9/bin/rc
# see also S+
. /usr/local/plan9/bin/9.rc

cur = `{basename  $%}
prev = `{sed -n '/^' ^ $cur ^ '([ 	]|$)/{; x; p; q; }; h' index}
if(~ $#prev 0) {
	echo 'no prev page' >[1=2]
	exit 'no prev page'
}
Slide $prev