3_60.scm

(load "3_59.scm")
(define (mul-series s1 s2)
  (cons-stream (* (stream-car s1) (stream-car s2))
               (add-streams (scale-stream (stream-cdr s2) (stream-car s1))
                            (mul-series (stream-cdr s1) s2))))

(define eulers-identity (add-streams (mul-series sine-series sine-series)
                                     (mul-series cosine-series cosine-series)))
;(stream-ref eulers-identity 0)