“…The nonlinear case is obviously more involved: spectral properties of (−∆) s p were studied in [4,17,18,21,30], a detailed regularity theory was developed in [3,24,25,28,29] (some results about Sobolev and Hölder regularity being only proved for the degenerate case p > 2), maximum and comparison principles have appeared in [12,27], while existence and multiplicity of solutions have been obtained for instance in [10,13,18,22,39] (see also the surveys [32,35]). For the purposes of the present study, we recall in particular [26], where it was proved that the local minimizers of the energy functional corresponding to problem (1.1) in the topologies of W s,p 0 (Ω) and of the weighted Hölder space C 0 s (Ω), respectively, coincide (namely, a nonlinear fractional analogue of the classical result of [5]).…”