1Barles, G., Chasseigne, E. and Imbert, C.. On the Dirichlet problem for second order elliptic integro-differential equations. Indiana Univ. Math. J. 57(1) (2008), 213–246.
2Barles, G., Chasseigne, E. and Imbert, C.. Hölder continuity of solutions of second-order nonLinear elliptic integro-differential equations. J. Eur. Math. Soc. (JEMS) 13(1) (2011), 1–26.
3Bellido, J. C. and Mora–Corral, C.. Existence for nonlocal variational problems in peridynamics. SIAM J. Math. Anal. 46(1) (2014), 890–916.
4Caffarelli, L. and Silvestre, L.. Regularity theory for nonlocal integro-differential equations. Comm. Pure Appl. Math 62(5) (2009), 597–638.
5Clarke, F. H.. Optimization and nonsmooth analysis. Classics in Applied Mathematics Appl. Math. 5 (1990).
6Di Castro, A., Kuusi, T. and Palatucci, G.. Local behavior of fractional p-minimizers. Ann. Inst. H. Poincaré Anal. Non Linéaire 33(5) (2016), 1279–1299.
7Di Neza, E., Palatucci, G. and Valdinoci, E.. Hitchhiker's guide to the fractional sobolev spaces. Bull. Sci. Math. 136(5) (2012), 521–573.
8Evans, L. C. and Gariepy, R.. Measure Theory and Fine Properties of Functions. Studies in Advanced Mathematics, (Boca Raton, Fl: CRC Press, 1992).
9Felmer, P. and Topp, E.. Uniform equicontinuity for a family of zero order operators approaching the fractional Laplacian. Comm. Partial Diff. Eq. 40(9) (2015), 1591–1618.
10Felsinger, M., Kassmann, M. and Voigt, P.. The Dirichlet problem for nonlocal operators. Math. Z. 279 (2015), 779–809.
11Ishii, H. and Nakamura, G.. A class of integral equations and approximation of p-Laplace equations. Calc. Var. PDE 37 (2010), 485–522.
12Rockafellar, R. T.. Clarke's tangent cones and the boundaries of closed sets in ℝn. Nonlinear. Anal. T.M.A. 3 (1979), 145–154.
13Rockafellar, R. T. and Wets, R. J. B.. Variational Analysis (Springer-Verlag, 1998).
14Ros–Oton, X. and Serra, J.. The Dirichlet Problem for the fractional laplacian: regularity up to the boundary. Journal de Mathématiques Pures et Appliquées 101(3) (2014), 275–302.
15Servadei, R. and Valdinoci, E.. Weak and viscosity solutions of the fractional Laplace equation. Publ. mat. 58(133) (2014), 154.
16Servadei, R. and Valdinoci, E.. The Brezis–Niremberg result for the fractional Laplacian. Trans. Am. Math. Soc. 367(1) (2015), 67–102.
17Silvestre, L.. Hölder estimates for solutions of integro-differential equations like the fractional Laplace. Indiana U. Math. J. 55(3) (2006), 1155–1174.