1. “Theory of linear operators in hilbert space.”;Ahiezer,1966
2. A quadratic form problem in the calculus of variations;Albert;Bull. Amer. Math. Soc.,1938
3. Matrices of linear operators;Anselone;Enseignement Math.,1963
4. Two-parameter eigenvalue problems in differential equations;Arscott;Proc. London Math. Soc.,1964
5. Boundary problems leading to orthogonal polynomials in several variables;Atkinson;Bull. Amer. Math. Soc.,1963