Perturbation of linear ordinary differential equations at irregular singular points

MR0243171 Sibuya, Yasutaka Yasutaka SIBUYA Perturbation of linear ordinary differential equations at irregular singular points Funkcialaj Ekvacioj. Serio Internacia 11 1969 235--246 http://fe.math.kobe-u.ac.jp/FE/Free/vol11/fe11-18.pdf http://fe.math.kobe-u.ac.jp/FE/FE_pdf_with_bookmark/FE11-20-en_KML/fe11-235-246/fe11-235-246.pdf http://www.ams.org/mathscinet-getitem?mr=MR0243171 fe11-235-246 1969 Perturbation of Linear Ordinary Differential Equations at Irregular Singular Points SIBUYA, Yasutaka SIBUYA, Yasutaka 1 Hsieh, P. F.; Sibuya, Y. Note on regular perturbations on linear ordinary differential equations at irregular singular points Funkcialaj Ekvacioj 8 1966 99-108 MR0203182 0203182 92 Cache/Hs/Hsieh,perturbations,Funkcialaj*,1966,1967 2 Sibuya, Y. Simplification of a system of linear ordinary differential equations about a singular point Funkcialaj Ekvacioj 4 1962 29-56 MR0152719 0152719 100 Cache/Si/Sibuya,Simplification,Funkcialaj*,1962,1963 3 Wasow, W. Asymptotic expansions for ordinary differential equations Interscience, New York 1965 MR0166448 Cache/Wa/Wasow,Asymptotic,Interscience,*,1965,1966