We present a new proof of the interiority of the policy function based on the Inada conditions. It is based on supporting properties of concave functions.

In an experiment, a group of strangers was randomly divided in pairs to play a prisoners’ dilemma; this process was indefinitely repeated. Cooperation did not increase when subjects could send public messages amounting to binding promises of future play.

We study a decentralized trading model as in Peters (1984a), where heterogeneous market participants face a trade-off between price and trade probability. We present a novel proof of existence of a unique demand vector in Nash equilibrium, based on a recursive approach that exploits the...