anchor.diff:  
   (defmethod object-rope ((object pov-matrix))
     (let ((elements (pov-matrix-elements object)))
  -    (with-pov-indent old-indent
  -      (declare (ignore old-indent))
  +    (with-pov-indent
         (let ((sep-1 (rope '|,| *pov-newline-indent*))
               (sep-0 '|, |))
           (rope '|matrix <|
  
positive.code:   list)
  
  (defmethod print-object ((object pov-block) stream)
    (with-pov-indent old-indent
      (format stream
              "~&~A~A {~&~{~&~A~}~&~A}"
              old-indent
              (pov-block-name object)
              (pov-block-list object)
              old-indent)))
  
  (defmethod object-rope ((object pov-block))
    (let ((rope (rope *pov-newline-indent*
                      (pov-block-name object)
                      '| {|)))
      (rope (with-pov-indent old-indent
              (declare (ignore old-indent))
              (fold (lambda (rope thing) (rope rope
                                               *pov-newline-indent*
                                               (object-rope thing)))
  
negative.code:                              x z y)))))
  
  (defmethod print-object ((object pov-matrix) stream)
    (let ((elements (pov-matrix-elements object))
          (old-indent *pov-indent*))
      (with-pov-indent
        (format stream "~&~Amatrix <~&~A~F, ~F, ~F,~&~A~F, ~F, ~F,~&~A~F, ~F, ~F,~&~A~F, ~F, ~F~&~A>"
                old-indent
                *pov-indent*
  