1. Persistance and smoothness of invariant manifolds for flows;Fenichel;Indiana Univ. Math. Journal,1971
2. Singular perturbations on the infinite interval;Hoppensteadt;Trans. Amer. Math. Soc.,1966
3. Differential Equations with Small Parameters and Relaxation Oscillations;Mishchenko,1980
4. Perturbation Methods;Nayfeh,1973
5. On the dependence of the solutions of differential equations on a small parameter;Tihonov;Mat. Sbornik,1948