PP-graphics with a nilpotent elliptic singularity in quadratic systems and Hilbert's 16th problem
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This paper is part of the program launched in (J. Differential Equations 110(1) (1994) 86) to prove the finiteness part of Hilbert’s 16th problem for quadratic system, which consists in proving that 121 graphics have finite cyclicity among quadratic systems. We show that any pp-graphic through a multiplicity 3 nilpotent singularity of elliptic type which does not surround a center has finite cyclicity. Such graphics may have additional saddles and/or saddle-nodes. Altogether we show the finite cyclicity of 15 graphics of (J. Differential Equations 110(1) (1994) 86). In particular we prove the finite cyclicity of a pp-graphic with an elliptic nilpotent singular point together with a hyperbolic saddle with hyperbolicity a1 which appears in generic 3-parameter families of vector fields and hence belongs to the zoo of Kotova and Stanzo (Concerning the Hilbert 16th problem, American Mathematical Society Translation Series 2, Vol. 165, American Mathematical Society, Providence, RI, 1995, pp. 155–201).