; my math

(define (factorial x)
    (if (equal? x 0)
        1
        (* x (factorial (- x 1)))))

(define (square x)
    (* x x))

(define (pow x y)
    (if (even? y)
        (if (= y 0)
            1
            (square (pow x (/ y 2))))
        (* x (square (pow x (/ (- y 1) 2))))))

(define (fib x)
    (cond
        ((= x 0) 1)
        ((= x 1) 1)
        (else (+ (fib (- x 1)) (fib (- x 2))))))