“…The nonlinear differential operator appearing in (1.1) is usually meant as a mean curvature operator in the Lorentz-Minkowski space and it is of interest in Differential Geometry and General Relativity [3,26,27]; it also appears in the nonlinear theory of Electromagnetism, where it is usually referred to as Born-Infeld operator [9,10,13]. In recent years, it has become very popular among specialists in Nonlinear Analysis, and various existence/multiplicity results for the associated boundary value problems are available, both in the ODE and in the PDE case, possibly in a non-radial setting (see, among others, [1,2,4,5,6,7,17,18,19,20,23,24,30] and the references therein).…”