On the Alexandrov–Balkeman–Pucci estimate for some nonlinear singular/degenerate elliptic operators

In this paper we show the Alexandrov–Bakelman–Pucci estimate for viscosity and weak solutions for some singular/degenerate nonlinear elliptic equations in the fully nonlinear and quasilinear contexts. We extend and refine the results obtained in [7, 22, 38]. Classical weak maximum principle results are recovered.