private void Normalize()
{
// compute greatest common divisor of numerator and denominator
BigInteger g = Numerator.Gcd(Denominator);
if (g.CompareTo(BigInteger.One) > 0)
{
Numerator = Numerator.Divide(g);
Denominator = Denominator.Divide(g);
}
if (Denominator.CompareTo(BigInteger.Zero) == -1)
{
Numerator = Numerator.Negate();
Denominator = Denominator.Negate();
}
}