Sharp upper bounds for splitting of separatrices near a simple resonance

General theory for the splitting of separatrices near simple resonances of near-Liouville-integrable Hamiltonian systems is developed in the convex real-analytic setting. A generic estimate [GRAPHICS] is proved for the Fourier coefficients of the splitting distance measure G(phi), phi epsilon T-n, describing the intersections of Lagrangian manifolds, asymptotic to invariant n-tori, epsilon being the perturbation parameter. The constants omega epsilon R-n, c(1) sigma > 0, c(2) epsilon R-n are characteristic of the given problem (the Hamiltonian and the resonance), cannot be improved and can be calculated explicitly, given an example. The theory allows for optimal parameter dependencies in the smallness condition for epsilon.