# convert to factorial(x);

tofactorial(binomial(n_,k_)) := n!/((n-k)!*k!);
tofactorial(gamma(x_)) := (x-1)!;
tofactorial(gamma(x_)/gamma(y_)) := (-1)^(y-x)*(-y)!/((-x)!);
tofactorial(psi(x_)/gamma(x_)) := (-1)^(-x+1)*(-x)!;
tofactorial(fallingfactorial(m_,n_)) := m!/((m-n)!);
tofactorial(risingfactorial(m_,n_)) := (m+n-1)!/((m-1)!);