anchor.diff:  (defmacro variable-level (x)
     `(car ,x))
   
  -(eval-when (eval compile load)
  +(eval-when (:compile-toplevel :load-toplevel :execute)
     (defmacro variable-value (x)
       #+include-name-in-variable `(cadr ,x)
       #-include-name-in-variable `(cdr ,x)))
  
positive.code: ;; dynamic variables used during compilation
  
  ;;; name of procedure being compiled
  (eval-when (eval compile load)
    (defvar name nil))				
  ;;; arity of procedure being compiled
  (defvar arity)					
  
negative.code:                   variables)
  		 form))))
  
  (eval-when (:compile-toplevel :load-toplevel :execute)
    (defmacro invisible-functor-p (x)
      `(get ,x 'invisible-functor)))
  
  