Suppose that I am infected with the COVID-19 virus. And at the start of some time period, t0, I am among N0 who are infected. We use the letter N for the number of people infected and t for time in days, and we use the subscript 0 to mean a particular starting time. Let us assume that there are no restrictions on my movement, or on the movement groups of people playing, attending events, going to the movies, shopping or relaxing on the beach with hundreds of others. So we can go out and be anyw
