■ 🕑 15. corrected exercise 1.3
   Updated to catch PhatCat's fix -- if x, y, and z are the same
   value, the code does not work
   
   (define (square x) 
     (* x x)) 
   (define (sum-squares x y) 
     (+ (square x) (square y))) 
     
   (define (sum-greater-squares x y z) 
     (if (> x y) 
         (if (> y z) 
             (sum-squares x y) 
             (sum-squares x z)) 
         (if (> x z) 
             (sum-squares y x)
             (if (= x y z)
                 (sum-squares x x)
                 (sum-squares y z)))))