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We discuss the existence of closed geodesic on a Riemannian manifold and the existence of periodic solution of second order Hamiltonian systems.

We prove that the linearization of a germ of holomorphic map of the type $F_{\lambda }\left(z\right)=\lambda (z+O\left(z^2\right))$ has a ${𝒞}^1$-holomorphic dependence on the multiplier $\lambda$. ${𝒞}^1$-holomorphic functions are ${𝒞}^1$-Whitney smooth functions, defined on compact subsets and which belong to the kernel of the $\overline{\partial }$ operator. The linearization is analytic for $\left|\lambda \right|\ne 1$ and the unit circle ${𝕊}^1$ appears as a natural boundary (because of resonances,roots of unity). However the linearization is still defined at most points of ${𝕊}^1$, namely those points which lie “far enough from resonances”,...