We construct a formal normal form for a class of real 2-codimensional submanifolds M ⊂ C N +1 defined near a CR singularity approximating the sphere. Our result gives a generalization of Huang-Yin's normal form in C 2 to a higher dimensional analogue case.
Keywords: normal form, CR singularity, Fischer decompositionwhere ϕ ′ m,n z ′ , z ′ is a bihomogeneous polynomial of bidegree (m, n) in z ′ , z ′ satisfying the following normalization conditionsA few words about the construction of the normal form. We want to find a formal biholomorphic map sending M into a formal normal form. This leads us to study an infinite system of homogeneous equations by truncating the original equation. As in the paper [14] of Huang-Yin, this system is a semi-non linear system and is very hard to solve. We have then to use the powerful Huang-Yin's strategy and defining the weight of z k to be 1 and the weight of z k to be s − 1, for all k = 1 . . . , N . Since Aut 0 (M∞) is infinite-dimensional, it follows that the homogeneous linearized normalization equations (see sections 3 and 4) have nontrivial kernel spaces. By using the preceding system of weights and a similar argument as in the paper [14] of Huang-Yin , we are able to trace precisely how the lower order terms arise in non-linear fashion: The kernel space of degree 2t + 1 is restricted by imposing a normalization condition on ϕ ′ ts+1,0 (z) and the kernel space of degree 2t + 2 by imposing normalization conditions on ϕ ′ ts,0 (z). The non-uniqueness part of the lower degree solutions are uniquely determined in the higher order equations.