1. On holomorphically similar matrices;Wasow;J. Math. Anal. and Appl.,1962
2. Simplification of turning point problems for systems of linear differential equations;Wasow;Trans. Amer. Math. Soc.,1963
3. Asymptotic solutions of a system of linear ordinary differential equations containing a parameter;Sibuya;Funkcialaj Ekvacioj,1962
4. Sur réduction analytique d'un système d'équations differentielles ordinaires linéares contenant un paramètre;Sibuya;Journal of the Faculty of Science, Univ. of Tokyo,1958