anchor.diff:  (defclass number (t) ())
   (defclass character (t) ())
   (defclass function (t) ())
  -(defclass hash-table (t) ())
  +;; (defclass hash-table (t) ()) defined below as a structure
   (defclass package (t) ())
   (defclass pathname (t) ())
   (defclass readtable (t) ())
  
positive.code:   (if (clos-instance-p x)
        (std-instance-class x)
        (built-in-class-of x)))
  
  (defun class-of-with-eql (object)
  	(or
  		(gethash object *clos-singleton-specializers*)
  		(class-of object)))
  
  ;;; N.B. This version of built-in-class-of is straightforward but very slow.
  ;;; This is only for booting, a faster method is used later -RGC
  
negative.code: ;;; N.B. To avoid making a forward reference to a (setf xxx) generic function:
  (defun setf-slot-value-using-class (new-value class object slot-name)
    (setf (slot-value-using-class class object slot-name) new-value))
  
  (defclass eql-specializer (standard-class) (object))
  
  (defun eql-specializer-p (x) (eq (class-of x) #.(find-class 'eql-specializer)))
  
  (progn
  
  