code: func (it *Fixed) Contains(ctx context.Context, v graph.Value) bool {
  	// Could be optimized by keeping it sorted or using a better datastructure.
  	// However, for fixed iterators, which are by definition kind of tiny, this
  	// isn't a big issue.
  	graph.ContainsLogIn(it, v)
  	vk := graph.ToKey(v)
  	for _, x := range it.values {
  		if graph.ToKey(x) == vk {
  			it.result = x
  			return graph.ContainsLogOut(it, v, true)
  		}
  	}
  	return graph.ContainsLogOut(it, v, false)
  }
docs: // Check if the passed value is equal to one of the values stored in the iterator.