R4RS 6.5.5  (+ number1 ...)  ==>  number
            (+)              ==>  number
            (* number1 ...)  ==>  number
            (*)              ==>  number

These procedures return the sum or product of their arguments.

(+ 3 4)  ==>  7
(+ 3)    ==>  3
(+)      ==>  0
(* 4)    ==>  4
(*)      ==>  1
