1.    Black,F and Litterman,R (1990)    "asset allocation: combining investors views with market equilibrium"
2.    Black,F and Litterman,R (1991)    "Global Asset Allocation with Equities,Bonds,and Currencies"
3.    Lee,W. (2000)                               "Advanced Theory and Methodology of Tactical Asset Allocation"
4     Satchell,S and Scowcroft,A (2000) "A demystification of the Black-Litterman Model: Managing Quantitative and Traditional Construction"

Thank you very much