european dominant position and american monopolization: a unifying approach from basic game theory

In this paper we explore the meaning of some fundamental legal definitions of Europeanand American antitrust using basic concepts of game theory. Important definitions in EU law likedominant position of a firm, abuse of such a dominant position, special responsibility of thedominant firm, or in US law like monopoly or monopolization offence, acquire more precisemeaning and operational content. Moreover they look closer than usually contended.In a competition game, in which there is a truly monopolistic/dominant firm (MDF) andcompetition law is respected, we state in a formal theorem that an MDF has a dominant strategy, soits choices should never be a source of ex post regret. Other players of the game, understanding andanticipating the realization of this dominant strategy, will optimize their behaviour taking it intoaccount and thus be more able to select a best solution among all possible outcomes.In this context which kind of behaviours can an MDF adopt to defend its market shares andeconomic position? Following the US Supreme Court and EU Court of Justice an MDF mustcompete using normal methods of competition, superior product or business acumen, therefore weargue that market power, whatever its origin, can be defended only through competition on themerit. This definition has practical consequences: unpredictable behaviours and actions that anormal firm would not adopt might be identified as illegal abuses of dominant position ormonopolization offences, also this idea is formalized in a theorem.