ref: ec8d7cdf024949d73c5f887f23f060cd33c1df28
dir: /sys/src/libsec/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