; your code goes here
 
(defclass a () ())
(defclass aa (a) ())
(defclass aaa (aa) ())
 
(defclass b () ())
(defclass bb (b) ())
 
(defgeneric m (x y))
 
(defmethod m ((x a)  (y b))  1)
(defmethod m ((x a)  (y bb)) 2)
(defmethod m ((x aa) (y b))  3)
 
(format t "~a ~a~%"
  (m (make-instance 'aa) (make-instance 'bb))
  (m (make-instance 'aa) (make-instance 'b)))
(format t "~a ~a~%"
  (m (make-instance 'aaa) (make-instance 'bb))
  (m (make-instance 'a)   (make-instance 'bb)))

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