(defclass person ()
  ((name :initarg :name :accessor person-name)))
(defmethod print-object ((self person) stream)
  (print-unreadable-object (self stream :identity t :type t)
    (format stream ":name ~S" (person-name self)))
  self)
(defparameter *author* (make-instance 'person :name "Pascal"))

*author* ; --> #<person :name "Pascal" #x30200277E7AD>

(setf (find-class 'employee) (find-class 'person))

*author* ; --> #<person :name "Pascal" #x302002599CAD>

(make-instance 'employee :name "Jean") ; --> #<person :name "Jean" #x3020026FE96D>

(defmethod salary ((self employee)) 40000)

(salary *author*) ; --> 40000