code: func DFS(t Traversal, f Iter, u T) bool {
  	lifo := NewLIFO(u)
  	for lifo.Size() > 0 {
  		next, _ := lifo.Pop()
  		if t.Visited(next) {
  			continue
  		}
  		if f(next) {
  			return true
  		}
  		for _, v := range t.Edges(next) {
  			lifo.Push(v)
  		}
  	}
  	return false
  }
docs: // DFS performs a depth first traversal calling f for each node starting from u.
  // If f returns true, traversal stops and DFS returns true.