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(define-class <A> <object> x y z)
(define a (make <A> (x 2) (y 4) (z 1)))
(y a)
;Value: 4 [Correct]

(define-class <B> <object> x y z)
(define b (make <B> (x 80) (y 21) (z 1000)))
(y b)
;Value: 21 [Correct]

(y a)
;Error: No method found -- APPLY-GENERIC-FUNCTION: y