anchor.diff:  (defun funinfo-add-free-var (fi var)
     "Add free variable."
     (push (funinfo-free-vars fi) var)
  -  nil)
  +  var)
   
   (defun funinfo-env-this (fi)
     "Get current environment description."
  
positive.code:   ; List of arguments.
    (args       nil)
  
    ; Argument expansion description.
    ;
    ; Tells, where arguments must be placed on the stack or if they must be
    ; placed on a rest list. This is used to insert argument passing instructions.
    ;(argument-places nil)
  
    ; Called functions.
    ;(callees nil)
  
    ; Total size of stack with arguments and local variables.
    ;(stack-size nil)
  
    ; List of variables defined outside the function.
    (free-vars  nil)
  
  
negative.code: 
  (defun funinfo-push-env (fi forms)
    "Open new environment."
    (push forms (funinfo-env fi)))
   
  (defun funinfo-pop-env (fi)
    "Close environment."
    (pop (funinfo-env fi)))
  
  (defun funinfo-env-add-args (fi args)
    "Add variables to the current environment."
    (setf (car (funinfo-env fi)) (append (car (funinfo-env fi)) args))
    args)
  
  (defun funinfo-env-add-arg (fi arg)
    "Add variables to the current environment."
  