E believes that all investors should optimize their portfolios a la Markowitz. M, on the other

hand, believes that a number of serious challenges exist for E's contention to be correct and has

suggested a labor capital component (a la Mayers) be included. R invokes the theory of

Rubinstein, Lucas, and Breeden and believes the foundations of E and extensions of M to be

incomplete. Comment on each of their assumptions, challenges, and models