(define prgs
'(
   ( 
      (procedure start
         (turn-right (if wall? (turn-left 
             (if wall? (turn-left (if wall? turn-left step)) step)) step)
                 put-mark start )
      )   
      (procedure turn-right (turn-left turn-left turn-left turn-left turn-left))
  )
  (
      (procedure start  (put-mark (if wall? turn-left step) start))
  )
  (
      (procedure start (step step step put-mark))
  )
)
)


(define pairs
'(
  (
   (((w w w w w w) 
     (w 0 w 0 w w) 
     (w 1 w 0 0 w) 
     (w 1 0 0 w w) 
     (w w w w w w)) 
     (1 3) southwest)

   (((w w w w w w) 
     (w 0 w 0 w w) 
     (w 0 w 0 0 w) 
     (w 0 0 0 w w) 
     (w w w w w w)) 
     (1 1) northeast)
   )
   (
   (((w w w w w w) 
     (w 0 w 0 w w) 
     (w 0 w 2 0 w) 
     (w 1 3 0 w w) 
     (w w w w w w)) 
     (3 3) northwest)

   (((w w w w w w) 
     (w 0 w 0 w w) 
     (w 0 w 0 0 w) 
     (w 0 0 0 w w) 
     (w w w w w w)) 
     (1 1) northeast)
  ))
 )