Consider the discrete points in time t_k for k = 1, 2,…, and let c_tk be the random variable that characterises the state of the system t_k. The family of random variables c_tk forms a stochastic process. The states at time t_k actually represent the (exhaustive and mutually exclusive) outcomes of the system at that time. The number of states may thus be finite or infinite. For example, the Poisson distribution indicated here represents a stochastic process with an infinite number of states. The random variable n represents the number of occurrences between 0 and t (assuming that the system starts at time 0). The states of the system at any time t are thus given by n = 0, 1, 2, …