@article{1183524689, author = {Erd\'elyi, A.}, title = {Singular perturbations}, journal = {Bull. Amer. Math. Soc.}, volume = {68}, number = {6}, year = {1962}, pages = { 420-424}, language = {en}, url = {http://dml.mathdoc.fr/item/1183524689} }
Erdélyi, A. Singular perturbations. Bull. Amer. Math. Soc., Tome 68 (1962) no. 6, pp. 420-424. http://gdmltest.u-ga.fr/item/1183524689/