Let us begin with a story: Once upon a time, there were two neighbouring soybean plantations. Five years in
succession, the plants showed symptoms of disease (diﬀerent each year). One plantation-owner was rich, and could aﬀord to consult the person who knew
more about soybean diseases than anyone else in the world. The other plantation-owner was poor, and had to seek advice elsewhere. Whereas the rich man could send his private jet to fetch the world-expert to his plantation, the poor man had to use the telephone or the postal service. And while one could pay for microscopic examinations, the other could not.