8.4.1
3. Evaluate the following expression step by step:
   (cond
     [(= 2 0) false]
     [(> 2 1)(symbol=? 'a 'a)]
     [else (= (/ 1 2) 9)])
 
==>(cond
     [false false]
     [(> 2 1)(symbol=? 'a 'a)]
     [else (= (/ 1 2) 9)])

==>(cond
     [(> 2 1)(symbol=? 'a 'a)]
     [else (= (/ 1 2) 9)])

==>(cond
     [true (symbol=? 'a 'a)]
     [else (= (/ 1 2) 9)])

==>(cond
     [true true]
     [else (= (/ 1 2) 9)])

==> All definitions successfully evaluated.