code: func (it *Or) Contains(ctx context.Context, val graph.Value) bool {
  	graph.ContainsLogIn(it, val)
  	anyGood, err := it.subItsContain(ctx, val)
  	if err != nil {
  		it.err = err
  		return false
  	} else if !anyGood {
  		return graph.ContainsLogOut(it, val, false)
  	}
  	it.result = val
  	return graph.ContainsLogOut(it, val, true)
  }
docs: // Check a value against the entire graph.iterator, in order.