1. Asymptotic expansions for ordinary differential equations;Wasow,1965
2. Singular perturbations in flight mechanics;Ardema;NASA TM X-62,1977
3. Ardema, M.D., Solution of second order linear system by matched asymptotic expansions, NASA TM 8.4, 246, to appear.
4. Systems of differential equations containing small parameter s multiplying some of the derivatives;Tihonov;Math. Sb.,1952
5. Asymptotic behavior of solutions to certain problems involving nonlinear differential equations containing a small parameter multiplying the highest derivatives;Vasileva;Russian Math. Surveys,1963