anchor.diff:        progn block
         * / < >
         mod sqrt sin cos atan exp round floor
  -      last copy-list nthcdr nth member mapcar elt length make-string string
  +      last copy-list nthcdr nth member mapcar elt length make-string
         make-array aref code-char char-code integer
         make-symbol make-package
         symbol-name symbol-value symbol-function symbol-package
  
positive.code:              (append (butlast tests) (list (cons t end)))
               tests))))
  
  (defun %%macroexpand (x)
    (? *macroexpand-hook*
        (funcall *macroexpand-hook* x)
  
negative.code: ;;; Things we have to implement ourselves.
  (defconstant +implementations+
      '(%set-atom-fun cpr rplacp %load atan2 pow quit string-concat %load
        %eval %defun early-defun %defvar %defmacro %string
        ? functional
        builtin? macro?
        %%macroexpand %%macrocall %%%macro?
  