anchor.diff:  
     (define-binder (:mval (var list) val decls body)
       (multiple-value-bind (vars bindings)
  -        (extract-nested-binding-specs var decls)
  +        (extract-nested-binding-specs var decls :extract-plain-lists t)
         `(multiple-value-bind ,vars ,val
            ,@(when-let (decl (mapcan (lambda (x) (use-declaration x decls)) vars))
                        `((declare ,@decl)))
  
positive.code:        (not (null symbol))
         (not (keywordp symbol))))
  
  (defun extract-nested-binding-specs (vars decls)
    (let ((bindings nil))
      (values
       (map-lambda-list
  
negative.code:       (lambda (list)
          (cond ((eql (car list) :mval)
                 (error "nested :MVAL in ~A are meaningless" vars))
                ((or extract-plain-lists (member (car list) *binder-specs*))
                 (let ((var-name (gensym (if extract-plain-lists
                                             "LIST-"
                                             (format nil "~A-" (car list))))))
                   (push (cons list var-name) bindings)
                   (values nil var-name)))
                (t (values t list)))))
  