Multiple orbits for hamiltonian systems on starshaped surfaces with symmetries
Il teorema D
In this paper the graphic planes where theorem D holds are considered. D is a special case of Desargues' theorem, occurring when two vertices of one of the homological triangles belong to a side of the other triangle. The main achievement is a unified proof of theorems by Moufang and Gleason; moreover, several characterizations of D are given and some algebraic properties of ternary rings are deduced.
Convergence results for periodic solutions of nonautonomous Hamiltonian systems
We prove some stability results for a certain class of periodic solutions of nonautonomous Hamiltonian systems in the case of Hamiltonian functions either with subquadratic growth or homogeneous with superquadratic growth. Thus we extend to the nonautonomous case some results recently established by the Authors for the autonomous case.
Periodic Solutions of Second Order Nonautonomous Systems with the Potentials Changing Sign
Some existence and multiplicity results for periodic solutions of second order nonautonomous systems with the potentials changing sign are presented. The proofs of the existence results rely on the use of a linking theorem and the Mountain Pass theorem by Ambrosetti and Rabinowitz [2]. The multiplicity results are deduced by the study of constrained critical points of minimum or Mountain Pass type.
Una caratterizzazione degli ampliamenti galoisiani
This paper deals with a characterization of arbitrary Galois extensions generalizing a well known characterization of algebraic Galois extensions.
Una condizione equivalente alla -transitività
In this paper a condition equivalent to -transitivity is given.
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