In the 70’s, Nekhorochev proved that for an analytic nearly integrable Hamiltonian system, the action variables of the unperturbed Hamiltonian remain nearly constant over an exponentially long time with respect to the size of the perturbation, provided that the unperturbed Hamiltonian satisfies some generic transversality condition known as steepness. Using theorems of real subanalytic geometry, we derive a geometric criterion for steepness: a numerical function $h$ which is real analytic around a...

We prove that every holomorphic bijection of a quasi-projective algebraic set onto itself is a biholomorphism. This solves the problem posed in [CR].

We study coherent subsheaves 𝓓 of the holomorphic tangent sheaf of a complex manifold. A description of the corresponding 𝓓-stable ideals and their closed complex subspaces is sketched. Our study of non-holonomicity is based on the Noetherian property of coherent analytic sheaves. This is inspired by the paper [3] which is related with some problems of mechanics.

We construct a non-polynomially convex compact subset of the unit torus in ${ℂ}^2$ with polynomially convex hull containing no analytic structure.

Soit $\omega$ un germe en $0\in {\mathbf{C}}^n$ de 1-forme différentielle holomorphe, satisfaisant la condition d’intégrabilité $\omega \wedge d\omega =0$ et non dicritique, i.e. sur toute surface $Z$ non intégrale de $\omega$, on ne peut tracer, au voisinage de 0, qu’un nombre fini de germes de courbes analytiques $({\Gamma }_i,P_i)$, intégrales de $\omega$, avec $P_i\in Z\cap Sing\omega$. Alors $\omega$ possède un germe d’hypersurface analytique intégrale.