anchor.diff:  ; tré – Copyright (c) 2009–2015 Sven Michael Klose <pixel@hugbox.org>
   
  -(declare-cps-exception %%objkey %%make-objkey %%numkey %make-href-object-key %href-key =-href-obj %href-==? hash-table? =-href)
  +(declare-cps-exception %%objkey %%numkey %make-href-object-key %href-key =-href-obj %href-==? hash-table? =-href)
   
   (defvar *obj-id-counter* 0)
   (defvar *obj-keys*       (%%%make-hash-table))
  
positive.code:        (return (%%%aref hash (%href-key !))))))
  
  (defun href (hash key)
    (!? hash.__tre-test
        (?
          (eq #'eq !)   (%%%aref hash (? (object? key)
                                         key.__tre-object-id
  
negative.code:         (%href-==? !) (%%%aref hash key)
          (%href-user hash key))
        (%%%aref hash key)))
  
  (defun hash-merge (a b)
    (when (| a b)
  