An elementary core equivalence theorem¶in a countable economy

We consider an infinite exchange economy with countably many traders, which can be regarded as a natural extension of finite exchange economies to an infinite one. In our countable economy the core defined in the traditional manner would be empty. To avoid this unwanted situation we have to strengthen the notion of “improves upon”. We will achieve this based on the idea that forming coalitions involve costs. Received: 23 August 2000 / Accepted: 12 April 2002 I am very grateful to István Dancs, Péter Medvegyev, Miklós Pintér, Csaba Sándor, András Simonovits, László Szili, Péter Tallos and the anonymous referees for comments and suggestions. Parts of this research were done during the author's Bolyai János Research Fellowship provided by the Hungarian Academy of Sciences (MTA). Of course, all errors remain the author's responsibility.