A very good book with the ideas of Jean-Marie Souriau on the fundamentals of mechanics.

Finally, a book in French on symplectic geometry! it is rare enough to be noticed.
The author presents the discovery, due to Lagrange, natural symplectic structure on the space
movements of a mechanical system. It clearly defines the application moment, shows the existence
refines an action involving a symplectic cocycle making the application equivariant moment.
Several important examples are presented. A stimulating book, an excellent preparation for the study of books
more extensive;