anchor.diff:  
   (defun expex-vm-go-nil (ex x)
     (with ((moved new-expr) (expex-filter-and-move-args ex (list .x.)))
  -    (values (apply #'append moved)
  -            `((%%vm-go-nil ,@new-expr ,..x.)))))
  +    (values moved `((%%vm-go-nil ,@new-expr ,..x.)))))
   
   (defun peel-identity (x)
     (? (identity? x)
  
positive.code: 
  (defun expex-make-return-value (ex s x)
    (let last (last x)
     	(if (expex-returnable? ex last.)
  		(append (butlast x)
  				(if (%setq? last.)
  					(if (eq s (second last.))
  				        (expex-guest-filter-setter ex last.)
  						(expex-make-setq-copy ex last s))
  				    (expex-make-%setq ex s last.)))
  		x)))
  
  (defun expex-atom-to-identity-expr (x)
  
negative.code:      x))
  
  (defun expex-expr (ex expr)
    (let x (? (named-lambda? expr) ; XXX remove?
  		    expr
  		    (expex-guest-filter-expr ex expr))
      (expex-cps x)
      (?
        (%%vm-go-nil? x)
          (expex-vm-go-nil ex x)
  	  (%var? x)
  