anchor.diff:    (let ((cell-coordinate 0)
           (cell-number 0))
       (map-over-block-cells
  -     #'(lambda (cell)
  -         (let ((size (aref sizes cell-number)))
  -           (block-adjust-cell* cell block
  -                               cell-coordinate common-coordinate
  -                               size common-size)
  -           (incf cell-coordinate (+ size spacing))
  -           (incf cell-number)))
  +     (lambda (cell)
  +       (let ((size (aref sizes cell-number)))
  +         (block-adjust-cell* cell block
  +                             cell-coordinate common-coordinate
  +                             size common-size)
  +         (incf cell-coordinate (+ size spacing))
  +         (incf cell-number)))
        block)))
   
   
positive.code: ;;; TODO:
  ;;;
  ;;; - Check types: RATIONAL, COORDINATE, REAL?
  ;;; - Better error detection.
  ;;; - Item list formatting.
  ;;; - Multiple columns:
  ;;; - - all columns are assumed to have the same width;
  ;;; - - all columns have the same number of rows; they should have the
  
negative.code: (defmethod map-over-row-cells (function
                                 (row-record standard-row-output-record))
    (map-over-output-records
     (lambda (record)
       (when (cell-output-record-p record) (funcall function record)))
     row-record))
  
  (defmacro formatting-row ((&optional (stream t)
  