anchor.diff:    (warn "RETRACT-INSTANCE is deprecated. Use RETRACT instead.")
     (parse-and-retract-instance instance (inference-engine)))
   
  -(defun assert-from-string (str)
  -  (eval (read-from-string str)))
  -
   (defun facts ()
     (let ((facts (get-fact-list (inference-engine))))
       (dolist (fact facts)
  
positive.code: ;;; File: language.lisp
  ;;; Description: Code that implements the LISA programming language.
  ;;;
  ;;; $Id: language.lisp,v 1.20 2002/11/21 14:53:22 youngde Exp $
  
  (in-package "LISA")
  
  
negative.code: (defmacro defimport (class-name)
    `(import-class-specification ',class-name))
  
  (defmacro defcontext (context-name &optional (strategy nil))
    `(unless (find-context (inference-engine) ,context-name nil)
       (register-new-context (inference-engine) 
                             (make-context ,context-name :strategy ,strategy))))
  
  (defmacro undefcontext (context-name)
    `(forget-context (inference-engine) ,context-name))
  