Stone, M. H. Irregular differential systems of order two and the related expansion problems. (English) JFM 51.0343.03 Bulletin A. M. S. 31, 225 (1925). Auszug aus einem Vortrag vor der American Mathematical Society. PDF BibTeX XML Cite \textit{M. H. Stone}, Bull. Am. Math. Soc. 31, 225 (1925; JFM 51.0343.03) Full Text: DOI