@Article{zbMATH03343118,
Author = {H. {Guggenheimer}},
Title = {{Geometric theory of differential equations. I: Second order linear equations}},
FJournal = {{SIAM Journal on Mathematical Analysis}},
Journal = {{SIAM J. Math. Anal.}},
ISSN = {0036-1410; 1095-7154/e},
Volume = {2},
Pages = {233--241},
Year = {1971},
Publisher = {Society for Industrial and Applied Mathematics (SIAM), Philadelphia, PA},
Language = {English},
MSC2010 = {34A30 34A26 34C05 34D20},
Zbl = {0216.10904}
}