code: func (it *And) subItsContain(ctx context.Context, val graph.Value, lastResult graph.Value) bool {
  	var subIsGood = true
  	for i, sub := range it.internalIterators {
  		subIsGood = sub.Contains(ctx, val)
  		if !subIsGood {
  			if lastResult != nil {
  				for j := 0; j < i; j++ {
  					it.internalIterators[j].Contains(ctx, lastResult)
  				}
  			}
  			break
  		}
  	}
  	return subIsGood
  }
docs: // Checks a value against the non-primary iterators, in order.