anchor.diff:  
   (defun singletonp (intset)
     "SINGLETONP intset => boolean"
  -  ;; MEMO: 2013-10-08 tkych
  +  ;; MEMO: 2013-10-08
     ;; The formula [ x & (x-1) ] remove the rightmost 1 from x.
     ;; If x is #b0, then return #b0.
     ;; e.g. (logand #b101010 (1- #b101010)) => #b101000
  
positive.code:   (bitmap 0 :type (integer 0 *)))
  
  (setf (documentation 'make-intset 'function)
        "MAKE-INTSET => new-intset")
  
  (defmacro make-new-intset (init-bitmap)
    (let ((new-intset (gensym "NEW-INTSET-")))
  
negative.code: 
  (defun intset:nset-difference (intset1 intset2)
    "intset:NSET-DIFFERENCE intset1 intset2 => modified-intset1"
    ;; MEMO: 2013-10-07
    ;; nset-difference may destroy list-1.
    ;; see. CLHS, function nset-difference
    (setf (bitmap intset1) (logandc2 (bitmap intset1)
  