Invariants of CR-manifolds associated with the tangent quadric
We construct a system of CR-invariants of a manifold generated by projective invariants of the tangent quadric. We present a description of the group of projective diffeomorphisms of a quartic. We also estimate the degree of a rational mapping of a quartic. The description problem for subgroups of a Cremona group of bounded degree is posed.
KeywordsManifold Rational Mapping Description Problem Projective Invariant Cremona Group
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