code: func (a *AttemptList) UpdateWith(o *AttemptList) {
  	for qid, atmpts := range o.To {
  		if curAtmpts, ok := a.To[qid]; !ok {
  			a.To[qid] = atmpts
  		} else {
  			curAtmpts.Nums = append(curAtmpts.Nums, atmpts.Nums...)
  			curAtmpts.Normalize()
  		}
  	}
  }
docs: // UpdateWith updates this AttemptList with all the entries in the other
  // AttemptList.