This article considers an externality that affects a broad range of markets, specifically markets where one set of firms sells some platform technology like a computer, video game console, or operating system, while another possibly overlapping set of firms sells peripherals compatible with that...

Antitrust law makes a sharp distinction between tacit and explicit collusion whereas the theory of repeated games -- the standard framework for studying collusion -- does not. In this paper, we study this difference in Stigler's (1964) model of secret price cutting. This is a repeated game with...