module language/ring

sig Node {next: Node, value: Value one -> Time}
sig Time {next: Time}
sig Value {}

fact {
	all n: Node | Node in n.^next
--	no ^next & iden
	no ^(Time <: next) & iden
	}
pred show () {  }
run show for 3 but exactly 3 Node, 0 Value, 0 Time