anchor.diff:              current-cell))))
   
   (defun ne (grid-world current-cell)
  +  "Move the robot north east by one cell in the grid world."
     (let ((new-x (- (car current-cell) 1))
           (new-y (+ (cdr current-cell) 1)))
       (list grid-world
  
positive.code:             current-cell))))
  
  (defun n-sensor (grid-world current-cell)
    (= (car current-cell) 0))
  
  (defun s-sensor (grid-world current-cell)
    (= (car current-cell) (- (car (array-dimensions grid-world)) 1)))
  
  (defun e-sensor (grid-world current-cell)
    (= (cdr current-cell) (- (cadr (array-dimensions grid-world)) 1)))
  
  (defun w-sensor (grid-world current-cell)
    (= (cdr current-cell) 0))
  
  (defun ne-sensor (grid-world current-cell)
    (and (n-sensor grid-world current-cell) (e-sensor grid-world current-cell)))
  
  (defun nw-sensor (grid-world current-cell)
    (and (n-sensor grid-world current-cell) (w-sensor grid-world current-cell)))
  
  (defun se-sensor (grid-world current-cell)
    (and (s-sensor grid-world current-cell) (e-sensor grid-world current-cell)))
  
  (defun sw-sensor (grid-world current-cell)
    (and (s-sensor grid-world current-cell) (w-sensor grid-world current-cell)))
  
  (setf dims '(5 5))
  
  (setf grid-world (make-grid-world dims))
  
  (setf current-cell (list (current-cell 2 2)
                           (current-cell 0 0)
                           (current-cell 4 4)
  
negative.code: ;               (se grid-world current-cell)
  ;               (sw grid-world current-cell)))
  
  ;; Set of conditionals/sensor programs.
  (setf conditionals '((n-sensor grid-world current-cell)
                       (w-sensor grid-world current-cell)
                       (e-sensor grid-world current-cell)
  