Communication, consensus and order. Who wants to speak first ?

Parikh and Krasucki [1990] showed that if rational agents communicate the value of a function f according to a protocol upon which they have agreed beforehand, they will eventually reach a consensus about the value of f, provided a fairness condition on the protocol and a convexity condition on the function f. In this article, we address the issue of how agents agree on a communication protocol in the case where they communicate in order to learn information. We show that if it is common knowledge among a group of agents that some of them disagree about two protocols, then the consensus value of f must be the same according to the two protocols.