1. Theory of Functional-Differential Equations;Hale,1977
2. Linear Differential Equations with a Delay Argument;Myshkis,1972
3. Sturm–Liouville Operators and their Applications;Marchenko,1977
4. Inverse Sturm–Liouville Problems;Levitan,1984
5. Inverse Sturm–Liouville Problems and their Applications;Freiling,2001