diff --git a/ch-13/2-displaying-a-pose/robot/arena.py b/ch-13/2-displaying-a-pose/robot/arena.py
index 17d4d98..dc317d4 100644
--- a/ch-13/2-displaying-a-pose/robot/arena.py
+++ b/ch-13/2-displaying-a-pose/robot/arena.py
@@ -20,27 +20,3 @@ target_zone = [
 
 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
diff --git a/ch-13/2-displaying-a-pose/robot/robot.py b/ch-13/2-displaying-a-pose/robot/robot.py
index 9992b44..433d8ec 100755
--- a/ch-13/2-displaying-a-pose/robot/robot.py
+++ b/ch-13/2-displaying-a-pose/robot/robot.py
@@ -17,7 +17,6 @@ ticks_per_revolution = encoder_poles * gear_ratio
 ticks_to_m = (wheel_circumference_mm / ticks_per_revolution) / 1000
 m_to_ticks = 1 / ticks_to_m
 
-wheel_separation_mm = 160
 
 motor_A2 = pwmio.PWMOut(board.GP17, frequency=100)
 motor_A1 = pwmio.PWMOut(board.GP16, frequency=100)
diff --git a/ch-13/3-moving-poses-with-sensors/robot/arena.py b/ch-13/3-moving-poses-with-sensors/robot/arena.py
index 17d4d98..dc317d4 100644
--- a/ch-13/3-moving-poses-with-sensors/robot/arena.py
+++ b/ch-13/3-moving-poses-with-sensors/robot/arena.py
@@ -20,27 +20,3 @@ target_zone = [
 
 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