The structure of optimal portfolio strategies for continuous time   markets
  The paper studies problem of continuous time optimal portfolio selection for a incom- plete market diffusion model. It is shown that, under some mild conditions, near optimal strategies for investors with different performance criteria can be constructed using a limited number of fixed processes (mutual funds), for a market with a larger number of available risky stocks. In other words, a dimension reduction is achieved via a relaxed version of the Mutual Fund Theorem. 
Nikolai Dokuchaev
q-fin.PM cs.SY math.OC math.PR