Function: factorial
Section: number_theoretical
C-Name: mpfactr
Prototype: Lp
Help: factorial(x): factorial of x, the result being given as a real number.
Doc: factorial of $x$. The expression $x!$ gives a result which is an integer,
 while $\kbd{factorial}(x)$ gives a real number.
Variant: \fun{GEN}{mpfact}{long x} returns $x!$ as a \typ{INT}.
