anchor.diff:    (declare (ignore _))
     (remove-if
       (lambda (b)
  -      (knows (a1 a b c)))
  +      (know (a1 a b c)))
       (remove-duplicates
         (remove-if-not #'plusp
            (list (+ a c) (abs (- a c)))))))
  
positive.code:   (declare (ignore _))
    (remove-if
      (lambda (c)
        (knows (b a b c)))
      (remove-duplicates
        (remove-if-not #'plusp
          (list (+ a b) (abs (- a b)))))))
  
negative.code:   (declare (ignore _))
    (remove-if
      (lambda (a)
        (know (c a b c)))
      (remove-duplicates
        (remove-if-not #'plusp
          (list (+ b c) (abs (- b c)))))))
  