?- flow( [
		[source, in, n1],
		[delay, n1, n2], 
		[delay, n2, n3], 
		[delay, n3, n4], 
		[coeff(0.2), n3, n1],
		[coeff(0.2), n3, n2],
		[coeff(0.2), n3, n3]
	],
	n3).