Elbert, Árpád; Garay, Barnabás M. (2006), "Differential equations: Hungary, the extended first half of the 20th century", in Horváth, János (ed.), A Panorama of Hungarian Mathematics in the Twentieth Century, I, Bolyai Soc. Math. Stud., vol. 14, Springer, Berlin, pp. 245–294, doi:10.1007/978-3-540-30721-1_9, MR2547513; see p. 248
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Elbert, Árpád; Garay, Barnabás M. (2006), "Differential equations: Hungary, the extended first half of the 20th century", in Horváth, János (ed.), A Panorama of Hungarian Mathematics in the Twentieth Century, I, Bolyai Soc. Math. Stud., vol. 14, Springer, Berlin, pp. 245–294, doi:10.1007/978-3-540-30721-1_9, MR2547513; see p. 248
Elbert, Árpád; Garay, Barnabás M. (2006), "Differential equations: Hungary, the extended first half of the 20th century", in Horváth, János (ed.), A Panorama of Hungarian Mathematics in the Twentieth Century, I, Bolyai Soc. Math. Stud., vol. 14, Springer, Berlin, pp. 245–294, doi:10.1007/978-3-540-30721-1_9, MR2547513; see p. 248