Blackwell Prediction for Categorical Data
  We study the problem of sequential prediction of categorical data and discuss a generalisation of Blackwell's algorithm on 0-1 data. The arguments are based on Blackwell's approachability results given in Blackwell, D. (1956): An Analog of the Minimax Theorem for Vector Payoffs, Pacific Journal of Mathematics, 6, 1-8. 
Hans Rudolf Lerche
math.ST stat.TH