func popRandom(set sets.String) string {
	list := set.List()
	sort.Strings(list)
	sel := list[rand.Intn(len(list))]
	set.Delete(sel)
	return sel
}
func popRandom(set sets.String) string {
	list := set.List()
	sort.Strings(list)
	sel := list[rand.Intn(len(list))]
	set.Delete(sel)
	return sel
}
// popRandom randomly selects an element of 'set' and pops it.