anchor.diff:  
   (in-package #:petalisp.examples.getting-started)
   
  -(defun present (expression &optional (view-graph nil))
  -  (when view-graph (petalisp.graphviz:view expression))
  -  (format t "~%=> ~A~%~%" (compute expression)))
  +(defun present (&rest arrays)
  +  (format t "~{~& => ~A~}"
  +          (multiple-value-list
  +           (apply #'compute arrays))))
   
   ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
   ;;;
  
positive.code:  (jacobi-2d
    (jacobi-2d domain)))
  
  ;;; Finally, let's have a glimpse at the Petalisp intermediate
  ;;; representation of Jacobi's algorithm.
  
  (petalisp.graphviz:view
   (first
    (petalisp.ir:ir-from-lazy-arrays
     (list
      (jacobi-2d
       (jacobi-2d domain))))))
  
negative.code:   (let ((interior (interior grid)))
      (fuse*
       grid
       (α #'* 1/4
          (α #'+
             (reshape grid (τ (i j) ((1+ i) j)) interior)
             (reshape grid (τ (i j) ((1- i) j)) interior)
  