anchor.diff:  (defun scan-object (object)
     "Scan one object, updating pointer fields."
     (case (%tag-field object)
  -    (0  (scan-error object)) ; even-fixnum
  -    (1  (scan-cons object))
  -    (2  (scan-symbol object))
  -    (3  (scan-array-header object))
  -    (4  (scan-error object)) ; unused
  -    (5  (scan-error object)) ; unused
  -    (6  (scan-error object)) ; unused
  -    (7  (scan-array-like object))
  -    (8  (scan-error object)) ; odd-fixnum
  -    (9  (scan-error object)) ; unused
  -    (10 (scan-error object)) ; character
  -    (11 (scan-error object)) ; single-float
  -    (12 (scan-function object))
  -    (13 (scan-error object)) ; unused
  -    (14 (scan-error object)) ; unbound-value
  -    (15 (scan-error object)) ; gc-forward
  +    (#.+tag-cons+
  +     (scan-generic object 2))
  +    (#.+tag-symbol+
  +     (scan-generic object 6))
  +    (#.+tag-array-header+
  +     (scan-generic object 4))
  +    (#.+tag-array-like+
  +     (scan-array-like object))
  +    (#.+tag-function+
  +     (scan-function object))
       (t (scan-error object))))
   
   (defun transport-error (object)
  
positive.code:   (emergency-halt "unscannable object"))
  
  (defun scan-generic (object size)
    (scavenge-many (ash (%pointer-field object) 4) size))
  
  (defun scan-cons (object)
    (scan-generic object 2))
  
  (defun scan-symbol (object)
    (scan-generic object 6))
  
  (defun scan-array-header (object)
    (scan-generic object 4))
  
  (defun scan-array-t (object)
    (let* ((address (ash (%pointer-field object) 4))
           (header (memref-unsigned-byte-64 address 0))
           (length (ldb (byte 56 8) header)))
      (when (hash-table-p object)
        (setf (hash-table-rehash-required object) 't))
      ;; 1+ to account for the header word.
      (scavenge-many address (1+ length))))
  
  (defun scan-stack-group (object)
    (let ((address (ash (%pointer-field object) 4)))
  
negative.code:     (with-gc-trace (object #\s)
        (scan-object object))))
  
  (defun sweep-static-space (space)
    (mumble "Sweeping static space")
    (let ((offset 0)
  