model source {
	component System(in i1, in i2, out o1) {
	   component Sub1(in i1, in i2, out o)
	   component Sub2(in i, out o)
	   i1 -> Sub1.i1
	   i2 -> Sub1.i2
	   Sub1.o -> Sub2.i
	   Sub2.o -> o1
	}
}