anchor.diff:  
   
   ;;--------------------------------------------------------------------
  -
  +;;
   ;; <intset> ::= [<bitmap>]
   ;; <bitmap> ::= (integer 0 *), e.g. 42 (<=> #b101010) ~ {1 3 5}
   
  
positive.code:   (let ((bm (bitmap intset)))
      (if (zerop bm)
          nil
          ;; MEMO: 2013-10-07 tkych
          ;; The formula [ x & -x ] extracts the rightmost 1 from x.
          ;; If x is #b0, then return #b0.
          ;; e.g. (logand #b101010 (- #b101010)) => #b10
  
negative.code:   (bitmap 0 :type (integer 0 *)))
  
  (setf (documentation 'make-intset 'function)
        "MAKE-INTSET => new-intset
  It returns a new empty intset.")
  
  (defmacro make-new-intset (init-bitmap)
    (let ((new-intset (gensym "NEW-INTSET-")))
  