“…Thus, even at the boundary, a viscosity interpretation seems to be the most convenient one in order to manage both existence and uniqueness questions. More precisely, throughout the paper we interpret solutions to (P ) λ to mean viscosity solutions defined in the next definition, introduced by De Silva [28, Definitions 2.2 and 2.3], and has been adopted in several subsequent works (see for instance [29,45,46]). If u, v : Ω → R are two functions and x ∈ Ω, by u ≺ x v we mean that u(x) = v(x) and u(y) ≤ v(y) in a neighborhood of x.…”