anchor.diff:              for fz  = (frontier-z  f)
               for fdw = (frontier-dw f) do
   
  -              (frontier-to-pool f)
  +              (free-frontier f)
   
                 (if (plusp fdw)
                     ;; Used? fdw actually seems to always be zero...
  
positive.code:   nil)
  
  
  (defun frontier-to-pool (f)
    "Add frontier F to the free frontier pool."
    (declare (type frontier f))
    (cons-and-frontier-to-pool (new-cons f)))
  
  
  
  
negative.code: 
  ;;;; ** free frontier pool
  
  (declaim (type list *frontier-pool*))
  (defvar *frontier-pool* nil)
  
  (eval-when (:load-toplevel :execute)
    (save-thread-initial-bindings *frontier-pool*))
  
  (declaim (inline new-cons-and-frontier
                   free-cons-and-frontier
                   free-frontier))
  
  (defun new-cons-and-frontier ()
    "Get a CONS and a FRONTIER from pool if available, and return them."
    (if-bind cell *frontier-pool*
      (progn
        (setf *frontier-pool* (rest cell)
              (rest cell) nil)
        cell)
      (cons^)))
  
  
  (defun free-cons-and-frontier (cell)
    "Add (first cell) - which must be a FRONTIER - to the free frontier pool."
    (declare (type cons cell))
    (setf (rest cell) *frontier-pool*
  