// "039.hac" -- should pass

// note: L2 has no direction specified, so may be send or receive, or both!
defproc sum_diff(chan?(int) L1, L2; chan!(int) R) {
int x, z, w;
chan(int) M;
chp {
	L1?(x), L2?(z);
	M!(x-z)
}
chp {
	M?(w);
	R!(w)
}
}

