julia> x = 2
2

julia> \"\"\"
        The factorial function.

        ```julia
        @assert fac(3) == 1 * 2 * 3
        ```
        \"\"\"
        function fac(n)
            if n < 2
                return 1
            else
                return n * fac(n - 1) # <-- recursive call
            end
        end


        # Lets try the function out...
        f(x + 1)
6
