anchor.diff:    ((sl-1)
      (sl-b)))
   
  +(typep (find-class 'singleton-1) 'singleton)
  +;; => T
  +
  +(subtypep (find-class 'singleton-1) 'singleton)
  +;; => T, T
  +
  +;; alternately ...
   (let ((c (find-class 'singleton-1)))
  -  ;;   (finalize-inheritance c)
     (multiple-value-bind (st-1 st-2)
         (subtypep c 'singleton)
       (multiple-value-bind (mt-1 mt-2)
  
positive.code: 
  (class-direct-slots (find-class 'singleton-2))
  
  
  )
  
negative.code: ;; => T, T, T, T
  
  
  (class-slots (find-class 'singleton-1))
  
  (class-direct-slots (find-class 'singleton-1))
  
  (defsingleton singleton-2 (singleton-1)
    ((sl-c)))
  