channel CIO {
	out payment(p:Int, purchase(x:Int)) == x
}

channel C1 {
	in payment(p1, update1(y)) == y
	out points(l:Int, update1(y)) == floor(y * 0.05)
}

channel C2 {
	in payment(p1, update2(z)) == z
	out history(h:List, update2(z)) == cons(z, h)
	out total(t:Int, update2(z)) == z + t
}