anchor.diff:        (withdraw (overdraft-account account) overdraft)
         (incf (balance account) overdraft))))
   
  -;; (defmethod withdraw :before ((account (eql *account-of-bank-president*)) amount)
  -;;   (let ((overdraft (- amount (balance account))))
  -;;     (when (plusp overdraft)
  -;;       (incf (balance account) (embezzle *bank* overdraft)))))
  +(defmethod withdraw :before ((account (eql *account-of-bank-president*)) amount)
  +  (let ((overdraft (- amount (balance account))))
  +    (when (plusp overdraft)
  +      (incf (balance account) (embezzle *bank* overdraft)))))
  +
  +;; -----------------------------------------------------------------------------
  +
  
positive.code: (defclass bank-account (account)
    (customer-name
     balance))
  
  (defclass checking-account (bank-account) ())
  
  
negative.code: 
  (defgeneric balance (account))
  
  (defmethod balance ((account bank-account))
    (slot-value account 'balance))
  
  (defgeneric withdraw (account amount)
    (:documentation "Withdraw the specified AMOUNT from the ACCOUNT.
  