anchor.diff:        function-source
         %number? == number== integer== character== %integer %+ %- %* %/ %< %>
         string== list-string
  -      =-aref
  +      %make-array =-aref
         %make-hash-table href =-href copy-hash-table hashkeys hremove
         ? functional
         builtin? macro?
  
positive.code: (defun builtin? (x) (gethash x *builtins*))
  (defun macro? (x) (rassoc x *macros* :test #'eq))
  
  (defun =-aref (v x &rest indexes) v x (apply #'aref x indexes))
  
  (defun %make-hash-table (&key (test #'eql))
  
negative.code: (defun hashkeys (x)
    (let ((n nil))
      (maphash #'(lambda (k v)
                   v
                   (push k n))
               x)
      n))
  