1. Singular Perturbations: Order Reduction in Control System Design,1972
2. Optimal Control;Athans,1966
3. Asymptotic Expansions;Erdélyi,1956
4. A note on singular perturbation of linear state regulators;Haddad;IEEE Trans. Automatic Control,1971
5. Singular perturbation of a class of two point boundary value problems arising in optimal control;Hadlock,1970