code: func (x *Pol) UnmarshalJSON(data []byte) error {
  	if len(data) < 2 {
  		return errors.New("invalid string for polynomial")
  	}
  	n, err := strconv.ParseUint(string(data[1:len(data)-1]), 16, 64)
  	if err != nil {
  		return err
  	}
  	*x = Pol(n)
  
  	return nil
  }
docs: // UnmarshalJSON parses a Pol from the JSON data.