In some applications, it is not sufficient for a computation to be merely carried out successfully at some time or the other. It is also necessary for it to be carried out within a specified time period, not sooner or later. One example of this is the computer systems that help control a space shuttle during takeoff. It is necessary for the computer to receive sensory data about thrust, tilt, altitude, velocity, air resistance, and the like, and make suitable changes at exactly the right time. Either too soon or too late could be disastrous. Another example is an automated assembly line where a robotic arm has to pick up an object off a moving conveyor belt. If the arm moves too soon, the object will not be there yet, and if the arm moves too late, then it will no longer be there. In either...