NUMBERP
=======

syntax: (numberp <object>) 

        ==> T | NIL

This function verifies, whether the object is a
number. A function is true (T), when its argument
is a number or a special kind of number, otherwise
it is false (NIL).

examples:      >(numberp #C(1 2))
               T

               >(numberp 3)
               T

               >(numberp pi)
               T

               >(numberp "a")
               NIL