anchor.diff:  ; to
   ; (defun foobar (A B C) (if C foo-body bar-body))
   
  -;(encapsulate
  -; ()
  -; (set-well-founded-relation l<) 
   (defun pdl-satisfies-aux (m w f worlds evaling-formula)
     (declare (xargs :well-founded-relation l<
                     :measure (list (acl2-count f) (acl2-count worlds))))
  
positive.code:             t
            (pdl-satisfies-aux m w f (cdr worlds) nil))
        nil)))
  ;)
  
  
  
  
negative.code: ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
  
  
  (defthm negation-semantics-correct
    (implies (and (modelp m)
                  (pdl-formulap m (get-prop-atoms m) (get-prog-atoms m))
                  (equal (first f) '~))
             (not (pdl-satisfies m w f))))
  
  
  
  