public static MathObject ExpandPower(this MathObject u, int n)
{
if (!(u is Sum))
{
return(u ^ n);
}
MathObject f = ((Sum)u).elts[0];
MathObject r = u - f;
MathObject s = 0;
int k = 0;
while (true)
{
if (k > n)
{
return(s);
}
int c =
Factorial(n)
/
(Factorial(k) * Factorial(n - k));
s = s + (c * (f ^ (n - k))).ExpandProduct(r.ExpandPower(k));
k++;
}
/*
* return u ^ n;
*/
}