y u no added by anonymous on Mon Nov 6 10:54:41 2017
(define (chr i j)
(case (array-ref arr i j)
((list +stuck-particle+) "X")
((list +moving-particle+) "*")
((list +empty-space+) " ")))
(define (chr i j)
(case (array-ref arr i j)
((list +stuck-particle+) "X")
((list +moving-particle+) "*")
((list +empty-space+) " ")))