# output nondeterministic.
resource summer()
	op sum (val int a) returns int result {call}
	op sender (val int a) {send}


	for [ i = 1 to 20 ] {
	    send sender (i)
	}


	proc sender (a)  {
		write(sum(a))
	}

	proc sum(a) returns result  {
		if (a == 0) {
			result = 0
		} else {
			result = a + sum(a-1)
		}
	}
end