Exercise 1.12: (back)

Scheme:

(define (pascal-triangle row col)
  (cond ((= col 0) 1)
        ((= row 1) 1)
        ((= col 1) 1)
        ((= row col) 1)
        (else (+ (pascal-triangle (- row 1) (- col 1))
                 (pascal-triangle (- row 1) col)))))