It is even worse than this, btw, as the markets are disjoint: there are two places to buy shoes, but virtually all customers shop at either one store or the oth

It is even worse than this, btw, as the markets are disjoint: there are two places to buy shoes, but virtually all customers shop at either one store or the other store (for practical reasons of cost and convenience that are similar to those seen with someone having to buy things from a store in a different physical region of the country than where they chose to live), making each store separately a monopoly over its relevant market.