  This is mainly a survey of recent work on algebraic ways to ``measure''
moduli spaces of connecting trajectories in Morse and Floer theories as well as
related applications to symplectic topology. The paper also contains some new
results. In particular, we show that the methods of a previous work
(http://fr.arXiv.org/find/math/1/barraud/0/1/0/2004/3/0) continue to work in
general symplectic manifolds (without any connectivity conditions) but under
the bubbling threshold.
