Semiconcavity of viscosity solutions for a class of degenerate elliptic integro-differential equations in $\mathbb R^n$ Chenchen Mou Indiana University Mathematics Journal 2016 text pdf 10.1512/iumj.2016.65.5921 10.1512/iumj.2016.65.5921 en Indiana Univ. Math. J. 65 (2016) 1891 - 1920 state-of-the-art mathematics http://iumj.org/access/