@Article{ gbegfg03, author = { Bellettini, Giovanni and Gronchi, Giovanni Federico }, title = { Barriers for systems of ordinary differential equations: an application to the two-body problem }, journal = { Rend. Atti Acc. Naz. Sci. XL Mem. Mat. }, year = { 2002 }, volume = { XXVI }, pages = { 145-160 }, URL = { http://cvgmt.sns.it/paper/966/ }, note = { cvgmt preprint} }