anchor.diff:      (values moved `((%%go-nil ,.x. ,@new-expr)))))
   
   (defun expex-expr-%=-0 (place val)
  -  (expex-import-variables place val)
  +  (expex-import-variable place)
     (with ((moved new-expr) (expex-move-args (list val)))
       (values moved (expex-make-%= place new-expr.))))
   
  
positive.code:   (!? (expex-variable-name x)
        (add-wanted-variable !)))
  
  (defun expex-import-variables (place val)
    (& *expex-import?*
       (when (import-variables?)
         (expex-import-variable place)
         (? (atom val)
            (expex-import-variable val)
            (adolist (.val)
              (expex-import-variable !))))))
  
  
  ;;;; GUEST CALLBACKS
  
negative.code: ;;;; MOVING ARGUMENTS
  
  (defun expex-filter-and-move-args (x)
    (expex-import-variables x)
    (with ((moved new-expr) (assoc-splice (filter #'expex-move (expex-guest-filter-arguments x))))
      (values (apply #'+ moved) new-expr)))
  
  