1. Differential and difference equation systems with a small parameter for the case in which the unperturbed (singular) system is in the spectrum;Butuzov;Diff. Equations,1970
2. Singular Systems of Differential Equations;Campbell,1980
3. On an assumption guaranteeing boundary layer convergence of singularly perturbed systems;Campbell;Automatica,1981
4. Consistent initial conditions for singular nonlinear systems;Campbell;Circuits, Systems, and Signal Processing,1982
5. Singular Systems of Differential Equations II;Campbell,1982