diff --git a/ch-13/1-modelling-space/computer/display_arena_from_robot.py b/ch-13/1-modelling-space/computer/display_from_robot.py
similarity index 100%
rename from ch-13/1-modelling-space/computer/display_arena_from_robot.py
rename to ch-13/1-modelling-space/computer/display_from_robot.py
diff --git a/ch-13/1-modelling-space/robot/arena.py b/ch-13/1-modelling-space/robot/arena.py
index 17d4d98..6e26d8a 100644
--- a/ch-13/1-modelling-space/robot/arena.py
+++ b/ch-13/1-modelling-space/robot/arena.py
@@ -17,30 +17,3 @@ target_zone = [
   [(1250, 1100), (1250, 900)],
   [(1250, 900), (1100, 900)],
 ]
-
-width = 1500
-height = 1500
-
-def point_is_inside_arena(point):
-  """Return True if the point is inside the arena"""
-  # cheat a little, the arena is a rectangle, with a cutout.
-  # if the point is inside the rectangle, but not inside the cutout, it's inside the arena.
-  # this is far simpler than any line intersection method.
-  
-  # is it inside the rectangle?
-  if point[0] < 0 or point[0] > width \
-    or point[1] < 0 or point[1] > height:
-    return False
-  # is it inside the cutout?
-  if point[0] > 1000 and point[1] < 500:
-    return False
-  return True
-
-def point_is_inside_target_zone(point):
-  """Return True if the point is inside the target zone"""
-  # cheat a little, the target zone is a rectangle.
-  # if the point is inside the rectangle, it's inside the target zone.
-  if point[0] < 1100 or point[0] > 1250 \
-    or point[1] < 900 or point[1] > 1100:
-    return False
-  return True