#
Representation of pairs using only numbers and arithmetic operations
^{
}

Show that we can represent pairs of nonnegative integers using only numbers and arithmetic operations if we represent the pair
`a`

and
`b`

as the integer that is the product
`2^a * 3^b`

. Give the corresponding definitions of the procedures
`cons`

,
`car`

, and
`cdr`

.

```
(define a 2)
(define b 3)
(define x (cons a b))
(define x2 (cons 0 1))
(define x3 (cons 1 0))
(check-equal? x 108)
(check-equal? x2 3)
(check-equal? x3 2)
(check-equal? (car x) a)
(check-equal? (cdr x) b)
(check-equal? (car x2) 0)
(check-equal? (cdr x2) 1)
(check-equal? (car x3) 1)
(check-equal? (cdr x3) 0)
```