1. Lectures on Elliptic Boundary Value Problems;Agmon,1965
2. Approximation by Hill functions;Babuška;Report University of Maryland,1969
3. Local spline approximation by moments;Birkhoff;J. Math. Mech.,1967
4. On uniform approximation by splines;de Boor;J. Approximation Theory,1968
5. A note on local spline approximation by moments;de Boor;J. Math. Mech.,1968