/// <summary>
/// Gets the greatest common divisor of two elements in a <see cref="IEuclideanDomain{T, TFirst, TSecond}"/> via Euclid's algorithm. The GCD of two elements <c>X</c> and <c>Y</c> is the unique minimal principal ideal.
/// </summary>
/// <typeparam name="T">The type of the carrier set.</typeparam>
/// <typeparam name="TFirst">The type of the first grouplike operation.</typeparam>
/// <typeparam name="TSecond">The type of the second groupike operation.</typeparam>
/// <param name="r">The ringlike structure.</param>
/// <param name="x">The first element.</param>
/// <param name="y">The second element.</param>
public static T Gcd <T, TFirst, TSecond>(this IEuclideanDomain <T, TFirst, TSecond> r, T x, T y)
where TFirst : ICommutativeGroup <T>
where TSecond : IMonoid <T>, ICommutative <T>
{
if (r.IsZero(x) || r.IsZero(y))
{
return(r.Zero <T, TFirst>());
}
while (!r.IsZero(y))
{
var t = y;
y = r.EuclideanDivide(x, y).remainder;
x = t;
}
return(x);
}
