1. Boundary layer problems exhibiting resonance;Ackerberg;Studies in Appl. Math.,1970
2. Chang, K. W. Approximate solutions of nonlinear boundary value problems involving a small parameter. SIAM J. Appl. Math.
3. Chang, K. W. Diagonalization method for a vector boundary value problem of singular perturbation type.
4. A boundary value problem for a nonlinear differential equation with a small parameter;Coddington;Proc. Amer. Math. Soc.,1952
5. Multiple solutions of singular perturbation problems;Cohen;SIAM J. Math. Anal.,1972