On the Number of Zeros of Abelian Integrals: A Constructive Solution of   the Infinitesimal Hilbert Sixteenth Problem
  We prove that the number of limit cycles generated by a small non-conservative perturbation of a Hamiltonian polynomial vector field on the plane, is bounded by a double exponential of the degree of the fields. This solves the long-standing tangential Hilbert 16th problem. The proof uses only the fact that Abelian integrals of a given degree are horizontal sections of a regular flat meromorphic connection (Gauss-Manin connection) with a quasiunipotent monodromy group. 
Gal Binyamini, Dmitry Novikov, Sergei Yakovenko