anchor.diff:      (error "classes don't agree"))
     (when method-class-p
       (cond ((symbolp method-class)
  -	   (let ((class (find-class method-class nil)))
  +	   (let ((class (sicl-environment:find-class method-class
  +						     environment)))
   	     (when (null class)
   	       (error "no such method class ~s" method-class))
   	     (setf method-class class)))
  
positive.code: 	   (error "method class must be a class or a name"))))
    (let ((remaining-keys (copy-list all-keyword-arguments)))
      (loop while (remf remaining-keys :generic-function-class))
      (if method-class-p
  	(apply #'reinitialize-instance generic-function
  	       :method-class method-class
  
negative.code:      &rest
         all-keyword-arguments
       &key
         environment
         (generic-function-class
  	(sicl-environment:find-class 'standard-generic-function environment))
         (method-class nil method-class-p)
       &allow-other-keys)
    (declare (ignore function-name))
    (cond ((symbolp generic-function-class)
  	 (let ((class (sicl-environment:find-class generic-function-class
  						   environment)))
  	   (when (null class)
  	     (error "no such generic-function-class ~s"
  		    generic-function-class))
  