anchor.diff:  
   ;;;; Diadic-Predicate-Test
   
  -(defclass diadic-predicate-test (prediate-test)
  +(defclass diadic-predicate-test (predicate-test)
     ((datum-a
       :initarg :datum-a
       :accessor test-datum-a)
  
positive.code:     :accessor test-pre-test-form)
     (pre-test-function
      :type function
      :initarg :setup-form
      :initform nil
      :accessor test-pre-test-function)
  
  
negative.code:                              (,form ,a ,b))))))
           (set-funcallable-instance-function instance fn)))
  
         (t (simple-style-warning "~<Unable to initialize PREDICATE-FUNCTION for ~S~> ~
  ~<Slot is not bound: ~S~>" instance 'test)))))
  
  #+NIL
  