■ 🕑 18. exercise 1.3
   [(define (square a)
       (* a a))
   
   (define (smallest x y z)
       (if (< x y)
           (if (< x z) x z)
           (if (< y z) y z)))
   
   (define (procedure x y z)
       (- (+ (square x)(square y)(square z))(square (smallest x y z))))
   
   (procedure 7 10 10)]