> 34-XX Ordinary differential equations > 34LXX Ordinary differential operators

34L05 General spectral theory	34L10 Eigenfunction expansions, completeness of eigenfunctions	34L15 Estimation of eigenvalues, upper and lower bounds
34L16 Numerical approximation of eigenvalues and of other parts of the spectrum	34L20 Asymptotic distribution of eigenvalues, asymptotic theory of eigenfunctions	34L25 Scattering theory
34L30 Nonlinear ordinary differential operators	34L40 Particular operators (Dirac, one-dimensional Schrödinger, etc.)	34L99 None of the above, but in this section

34LXX Ordinary differential operators