John Hornstein has written about the author's theorem on
nonintegrability of geodesic flows on closed surfaces of genus greater
than one: "Here is an example of how differential geometry, differential
and algebraic topology, and Newton's laws make music together" (Amer.
Math. Monthly, November 1989).
Kozlov's book is a systematic introduction to the problem of exact
integration of equations of dynamics. The key to the solution is to find
nontrivial symmetries of Hamiltonian systems. After Poincaré's work it
became clear that topological considerations and the analysis of
resonance phenomena play a crucial role in the problem on the existence
of symmetry fields and nontrivial conservation laws.