Ceteris paribus, three industries are identical except that in industry A there are six firms that produce a homogeneous product, in B there are six firms that produce differentiated products that are all good substitutes for each other, while in C there are six firms that produce differentiated products but competition between them is localized-each firm only has two competitors that produce a good substitute. In which industry is collusion likely more sustainable? How is this related to market definition?