“…In the case that U is not concave, problem (1.1) is more involved. There is a broad class of models in which the non-concave problem has been studied by reducing it to the classical concave case; see for instance Aumann and Perles [2], Carpenter [18], Berkelaar et al [8], Larsen [31], Carassus and Pham [15], Rieger [35], Basak and Makarov [5] and Bichuch and Sturm [13]. At the other end of the scale, there are results on the existence of a solution in a number of (incomplete) discrete-time settings where one does not necessarily have a fixed pricing density, but the structure of the setup allows one to optimize directly over the set of strategies; see Benartzi and Thaler [7], Bernard and Ghossoub [10], He and Zhou [23] and Carassus and Rásonyi [16].…”