elevator control system

You will specify the behavior of a software system to be installed to control a simple elevator system. The elevator services a three-floor building. Inside the elevator there are request buttons, one for each floor. If the user inside the elevator presses a button, the elevator will visit the corresponding floor and open its doors. Floor 1 and floor 3 each has a request button that a user presses to command the elevator to come to that floor and to open its doors. Floor 2 has two request buttons to indicate which direction (up or down) the user will want to be taken once they are inside the elevator. If the elevator’s doors open, they should stay open for five time units. The elevator has two buttons to open and close the doors. When any of these buttons is pressed, the button will light up until the request is responded. You should not make any assumptions about how much time it takes the elevator to move between floors. At the very least, you should make sure that the following properties hold in your system with the help of a verification tool. 1. Requests to be delivered to a particular floor are eventually serviced 2. The elevator never moves with its doors open