Each individual in a population independently has a random number of offspring
that is Poisson distributed with mean λ. Those initially present constitute
the zeroth generation. Offspring of zeroth generation people constitute the first
generation; their offspring constitute the second generation, and so on. If Xn
denotes the size of generation n, is {Xn,n ≥ 0} a Markov chain. If it is, give its
transition probabilities Pi,j ; if it is not, explain why it is not
