Exercise 2.56: Show how to extend the basic
differentiator to handle more kinds of expressions.  For instance, implement
the differentiation rule

  
    
      
        d
        (
        
          u
          
            
            n
          
        
        )
      
      
        d
        x
      
    
  
  
  =
  
  
    n
    
      u
      
        
        n
        −
        1
      
    
    
    
      
        
          d
          u
        
        
          d
          x
        
      
    
  

by adding a new clause to the deriv program and defining appropriate
procedures exponentiation?, base, exponent, and
make-exponentiation.  (You may use the symbol ** to denote
exponentiation.)  Build in the rules that anything raised to the power 0 is 1
and anything raised to the power 1 is the thing itself.