In the previous exercise we defined a reference system (A [math]\theta[/math]) for the robot, and defined the wheel position and its outline. Now we are going to add the positions for the sensors. The Thymio robot has a total of 9 optical proximity sensors: [list] [*] 2 ground optical sensors [math](C_0, C_1)[/math] [*] 5 horizontal forward proximity sensors [math](D_0, D_1, D_2, D_3, D_4)[/math] [*] 2 horzontal backward proximity sensors [math](D_5, D_6)[/math] [/list] The center of the circular arc does not lie on the pen hole. Try to find where it is. You can use a perpendicular bisector on points [math](B_1, B_2, B_3)[/math] to find it.