@article{01209884,
title = {Critical case of multiple pairs of pure imaginary roots of a nonautonomous essentially nonlinear },
journal = {Memoirs on Differential Equations and Mathematical Physics},
volume = {12},
year = {1997},
pages = {145-149},
zbl = {0912.34046},
language = {en},
url = {http://dml.mathdoc.fr/item/01209884}
}
Vitrichenko, I. Critical case of multiple pairs of pure imaginary roots of a nonautonomous essentially nonlinear . Memoirs on Differential Equations and Mathematical Physics, Tome 12 (1997) pp. 145-149. http://gdmltest.u-ga.fr/item/01209884/