1. S. Agmon, A. Douglis, and L. Nirenberg, “Estimates near the boundary for solutions of elliptic partial differential equations satisfying general boundary conditions. I,” Commun. Pure Appl. Math., 12, 623–727 (1959).
2. M. S. Agranovich and M. I. Vishik, “Elliptic problems with a parameter and parabolic problems of general type,” Uspekhi Mat. Nauk, 19, No. 3, 53–161 (1964); English transl.: Russian Math. Surveys, 19 (1964).
3. W. G. Bade and R. S. Freeman, “Closed extensions of the Laplace operator determined by a general class of boundary conditions,” Pacific J. Math., 12, No. 2, 395–410 (1962).
4. R. Beals, “Nonlocal elliptic boundary-value problems,” Bull. Amer. Math. Soc., 70, No. 5, 693–696 (1964).
5. A. Bensoussan, “On the Hamilton-Jacobi approach for the optimal control of diffusion processes with jumps,” in: Stochastic Analysis (A. Freedman, M. Pinsky, Eds). Academic Press, New York, 25–55 (1978).