ref: cbc397384e190d18c4419de7ca59f8b10a6a84dc
dir: /sys/src/libmp/port/reduce/
O=$1
shift
objtype=$1
shift
if(ls -p ../$objtype/*.[cs] >[2]/dev/null | sed 's/..$//;s/^/^/' > /tmp/reduce.$pid) {
	echo $* | tr ' ' \012 | grep -v -f /tmp/reduce.$pid | tr \012 ' '
}
if not {
	# if empty directory, just return the input files
	echo $*
}
rm /tmp/reduce.$pid