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@article{MAN_1913__74_158624, author = {G.D. Birkhoff}, title = {Equivalent {Singular} {Points} of {Ordinary} {Linear} {Differential} {Equations}}, journal = {Mathematische Annalen}, pages = {134--139}, publisher = {mathdoc}, volume = {74}, year = {1913}, zbl = {44.0373.01}, url = {http://geodesic.mathdoc.fr/item/MAN_1913__74_158624/} }
G.D. Birkhoff. Equivalent Singular Points of Ordinary Linear Differential Equations. Mathematische Annalen, Tome 74 (1913), pp. 134-139. http://geodesic.mathdoc.fr/item/MAN_1913__74_158624/