anchor.diff:              finally (return fitness)))
       0))
   
  +;; Fitness function that maps the fitness helper across the results list.
   (defun fitness-function (results)
     (apply #'+ (mapcar #'fitness-helper results)))
   
  
positive.code:                      (se-sensor grid-world current-cell)
                       (sw-sensor grid-world current-cell)))
  
  (defun wall-cell-p (grid-world cell)
    (let ((dimensions (array-dimensions grid-world)))
      (or (= (car cell) 0)
  
negative.code:             current-cell))))
  
  (defun w (grid-world current-cell)
    "Move the robot west by one cell in the grid world."
    (let ((new-y (- (cdr current-cell) 1)))
      (list grid-world
            (if (>= new-y 0)
  