The term "controlling light" is defined as follows:

Briefly explain initial state

traffic light is installed at a junction of a railroad and a road. the traffic light is controlled by two switches in the rails placed one mile apart on either side of the junction. a switch is turned on when the train is over it and is turned off otherwise. the traffic light changes from green (logic 0) to red (logic 1) when the beginning of the train is one mile from the junction. the light changes back to green when the end of the train is one mile away from the junction. all trains are less than 2 miles long. Draw circuit diagram

Purpose: The entry/Exit of the parking lot is a single lane passage. By controlling the indicators, the program ensures that only one car can pass through the Entry/Exit so as to prevent car accident between entering and leaving cars. Y1 X1 Program Description: In the parking lot, there are two light indicators individually directing the entering and leaving cars. By the interlock control circuit, only one indicator will show "GO" signal and the car accident will thus be prevented. When an the same time, the leaving car indicator will show "STOP". Car entering is allowed but leaving is prohibited in this case. When a leaving car draws near the vehicle control barrier, X1 will be ON and so will Y1. The leaving car indicator will show "GO" and the entering car indicator will show "STOP"| draws near the vehicle control barrier, XO will be ON and so will YO. The entering car indicator will show "GO". At TOP GO