Alexandroff–Bakelman–Pucci estimate for singular or degenerate fully nonlinear elliptic equations

We prove the classical Alexandroff–Bakelman–Pucci estimate for fully nonlinear elliptic equations involving singular or degenerate operators having as models | p | α M λ , Λ ± ( X ) , where M λ , Λ ± are the Pucci extremal operators with parameters 0 < λ ⩽ Λ and α > − 1 .