code: func (tx *Tx) AscendEqual(index, pivot string,
  	iterator func(key, value string) bool) error {
  	var err error
  	var less func(a, b string) bool
  	if index != "" {
  		less, err = tx.GetLess(index)
  		if err != nil {
  			return err
  		}
  	}
  	return tx.AscendGreaterOrEqual(index, pivot, func(key, value string) bool {
  		if less == nil {
  			if key != pivot {
  				return false
  			}
  		} else if less(pivot, value) {
  			return false
  		}
  		return iterator(key, value)
  	})
  }
docs: // AscendEqual calls the iterator for every item in the database that equals
  // pivot, until iterator returns false.
  // When an index is provided, the results will be ordered by the item values
  // as specified by the less() function of the defined index.
  // When an index is not provided, the results will be ordered by the item key.
  // An invalid index will return an error.