It is not infrequent to see studies of imperfect competition or of industrial organization rest upon questionable foundations such as the hypothesis that inverse market demand is, whenever it is positive, concave or even linear. Assumptions of this sort are not robust (i.e., "additive") in the...

The first part of the paper is a brief introduction to the concepts and methods used in recent endogenous business cycles models. Endogenous deterministic and stochastic fluctuations are bound to occur, under increasingly plausible assumptions, in models with individual optimization, market...