BRAUN, Martin. Differential equations and their applications : an introduction to applied mathematics. 4th ed. New York [u.a.] : Springer, c1993. 578 s. Texts in applied mathematics ; 11. Available on Internet: <http://www.gbv.de/dms/hebis-darmstadt/toc/24052132.pdf> <http://www.zentralblatt-math.org/zmath/en/search/?an=0771.34001> ISBN 0-387-97894-1.