1. Inverse Sturm–Liouville Problems and their Applications;Freiling,2001
2. Sturm–Liouville Operators and their Applications;Marchenko,1986
3. Inverse Sturm–Liouville Problems;Levitan,1987
4. Theory of Functional Differential Equations;Hale,1977
5. Linear Differential Equations with a Delay Argument;Myshkis,1972