anchor.diff:  ;;; Resolution-based Q&A system.
   ;;;
   ;;; Pranav Ravichandran <me@onloop.net>
  +
  +(defstruct
  +  (var
  +    (:constructor var (x))) x)
   
   (defstruct
     (fact
  
positive.code:     (:constructor defwff (operator wffs)))
    operator wffs)
  
  (defun cnf-rule (facts implications)
    (defwff 'or (demorgan (defwff 'not facts)) (demorgan implications)))
  
  (defun demorgan (wff &aux
                       (operator (if (wff-p wff) (wff-operator wff)))
  
negative.code:           ((notevery #'fact-p operand)
             (defwff operator (mapcar #'(lambda (x) (demorgan x)) operand)))
            ('else wff))))
  
  (defun resolve (facts rules goal)
    ())
  