“…Papers and books [18,32,33,34,35,36,43,44,47,48,52,53,54,55,56,57,58,63,69] present various PDE, analytic and probabilistic approaches and connections with stochastic optimal control. The theory of viscosity solutions was introduced in [68,71,72] and its general theory was further developed in [2,3,4,11,12,15,16,17,19,23,24,25,37,40,41,70]. In particular, papers [24,70] contain higher order regularity results for viscosity solutions.…”