12

Exercise 1.12: The following pattern of numbers is called Pascal’s triangle.

         1
       1   1
     1   2   1
   1   3   3   1
 1   4   6   4   1
       . . .

The numbers at the edge of the triangle are all 1, and each number inside the triangle is the sum of the two numbers above it. Write a procedure that computes elements of Pascal’s triangle by means of a recursive process.

(define (P row col) (cond ((= col 1) 1) ((= row col) 1) (else (+ (P (- row 1) (- col 1)) (P (- row 1) col)))))

(P 5 1)

(P 5 2)