1. Estimates near the boundary for solutions of elliptic partial differential equations satisfying general boundary conditions: I;Agmon;Commun. Pure Appl. Math.,1959
2. S. Dahlke, E. Novak, W. Sickel, Optimal approximation of elliptic problems by linear and nonlinear mappings I, J. Complexity, to appear, see also the paper associated with the talk of E. Novak at: http://www.dagstuhl.de/04401/Materials/
3. S. Dahlke, E. Novak, W. Sickel, Optimal approximation of elliptic problems by linear and nonlinear mappings II, preprint.
4. Optimization in Solving Elliptic Problems;D’yakonov,1996
5. Lower bounds for the complexity of Monte Carlo function approximation;Heinrich;J. Complexity,1992