anchor.diff:  
   
   (defun smt-plan-encode (state-vars concrete-actions
  -                        initial-true initial-false
  +                        initial-state
                           goal
                           steps)
     (let* ((smt-statements nil)
  
positive.code:             (declare-step v ))))
  
        ;; initial state
        (dolist (p initial-true)
          (stmt (smt-assert (format-state-variable p 0))))
        (dolist (p initial-false)
          (stmt (smt-assert (smt-not (format-state-variable p 0)))))
        ;; goal state
        (stmt (smt-assert (rewrite-exp goal steps)))
        ;; operator encodings
  
negative.code:     (assert i)
      i))
  
  (defun state-vars-ref (state-vars i)
    (nth i state-vars))
  
  (defun state-vars-size (state-vars)
    (length state-vars))
  
  