An electronic circuit is created to light a lamp. There are two buttons (named A and B) in the circuit, each of which can create a "short-to-ground" that will result in the lamp failing to light when pressed. List all of the possibilities for the state of the two buttons (pressed or not pressed) at any given moment. Assuming each of these are equally likely, what is the probability that the lamp lights in a given moment? What is the probability that the lamp fails to light