The Bellman function of two variables for the dyadic maximal operator
  For p>1 we find the Bellman function of two variables associated with the dyadic maximal operator on Rn.Actually we do that in the more general setting of tree-like maximal operators.We provide a simple and elementary proof,different from those in [4] and [9]. 
Eleftherios N. Nikolidakis, Antonios D. Melas
math.FA