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We are interested on families of formal power series in $\text{(}{ℂ}^{},0\text{)}$ parameterized by ${ℂ}^n$ ($\widehat{f}={\sum }_{m=0}^{\infty }{P}_m(x_1,\cdots ,x_n)x^m$). If every $P_m$ is a polynomial whose degree is bounded by a linear function ($deg{P}_m\le Am+B$ for some $A\>0$ and $B\ge 0$) then the family is either convergent or the series $\widehat{f}(c_1,\cdots ,c_n,x)\notin ℂ\left\{x\right\}$ for all $(c_1,\cdots ,c_n)\in {ℂ}^n$ except a pluri-polar set. Generalizations of these results are provided for formal objects associated to germs of diffeomorphism (formal power series, formal meromorphic functions, etc.). We are interested on describing the nature of the set of parameters where...

The formal class of a germ of diffeomorphism $\varphi$ is embeddable in a flow if $\varphi$ is formally conjugated to the exponential of a germ of vector field. We prove that there are complex analytic unipotent germs of diffeomorphisms at ${ℂ}^n$ ($n\>1$) whose formal class is non-embeddable. The examples are inside a family in which the non-embeddability is of geometrical type. The proof relies on the properties of some linear functional operators that we obtain through the study of polynomial families of diffeomorphisms...