[Boost-users] factorial function

Hi everyone, I'm new to boost (and not so new but not very experienced to c++) and I'm having problems with functions defined with a template, as factorial (http://www.boost.org/doc/libs/1_38_0/libs/math/doc/sf_and_dist/html/math_too...). My questions is, how do I call the funtion factorial? Why isn't it enough calling factorial(n) where n is an unsigned integer? Does one need to define the function specifying the result type before? If so, how? Thanks in advance. Greetings, Alberto.