}
func (e posetEdge) Target() uint32 { return uint32(e) >> 1 }
func (e posetEdge) Strict() bool   { return uint32(e)&1 != 0 }
func (e posetEdge) String() string {
	s := fmt.Sprint(e.Target())
	if e.Strict() {
		s += "*"
	}
	return s
}

// posetNode is a node of a DAG within the poset.
type posetNode struct {
	l, r posetEdge
}

// poset is a union-find data structure that can represent a partially ordered set