“…Problem (1.4) arises from many branches of mathematics and applied mathematics and has been discussed by many authors and in many contexts, see, for instance, [1,3,7,13,[16][17][18]23,25,[31][32][33][34][35][36]39,42,44,45,49,50] and the references therein. For b ≡ 1 in Ω: when f (u) = e u and N = 2, problem (1.4) was studied much earlier.…”