code: func isNationalNumberSuffixOfTheOther(firstNumber, secondNumber *PhoneNumber) bool {
  	var (
  		firstNumberNationalNumber = strconv.FormatUint(
  			firstNumber.GetNationalNumber(), 10)
  		secondNumberNationalNumber = strconv.FormatUint(
  			secondNumber.GetNationalNumber(), 10)
  	)
  	// Note that endsWith returns true if the numbers are equal.
  	return strings.HasSuffix(firstNumberNationalNumber, secondNumberNationalNumber) ||
  		strings.HasSuffix(secondNumberNationalNumber, firstNumberNationalNumber)
  }
docs: // Returns true when one national number is the suffix of the other or both
  // are the same.