Exercise 3.57: How many additions are performed
when we compute the 
  
    n
    
      th
    
  
 Fibonacci number using the definition of
fibs based on the add-streams procedure?  Show that the number of
additions would be exponentially greater if we had implemented (delay ⟨exp⟩) 
simply as (lambda () ⟨exp⟩), without using the
optimization provided by the memo-proc procedure described in 
3.5.1.192