@Book{zbMATH03572563,
Author = {Robert {Hermann}},
Title = {{The geometry of non-linear differential equations, B\"acklund transformations, and solutions. Part A}},
FJournal = {{Interdisciplinary Mathematics}},
Journal = {{Interdisciplinary Math.}},
Volume = {12},
Year = {1976},
Publisher = {Math Sci Press, Brookline, MA},
Language = {English},
MSC2010 = {35-02 35A30 35A22 35G20 58A15},
Zbl = {0367.35001}
}