anchor.diff:  (defclass defsys:standard-system (defsys:name-mixin defsys:hash-table-mixin defsys:system)
     ())
   
  -(defvar *root-system* (make-instance 'defsys:standard-system :name 'defsys:system))
  +(defclass %root-system (defsys:standard-system) ())
  +
  +(defvar *root-system* (make-instance '%root-system :name 'defsys:system))
   
   (defun defsys:root-system ()
     *root-system*)
  
positive.code:   (:method ((system-name symbol) definition-name environment args &rest options)
      (apply #'defsys:expand-definition
             (defsys:locate *root-system* system-name)
             definition-name environment args options)))
  
  (defmacro defsys:define ((kind definition-name &body options)
                           &body args &environment env)
  
negative.code:                    definition-name :errorp errorp))
    (:method ((system defsys:hash-table-mixin) definition-name &key (errorp t))
      (declare (ignore errorp))
      (identity (gethash definition-name (slot-value system '%hash))))
    (:method ((system %root-system) definition-name &key (errorp t))
      (declare (ignore errorp))
      (if (eq definition-name 'defsys:system)
          system
          (call-next-method))))
  
  (defgeneric (setf defsys:locate) (new-definition system definition-name &key errorp)
    (:method (new-definition (system-name symbol) definition-name &key (errorp nil))
  