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Twin positive periodic solutions of second order singular differential systems
(Uniwersytet Mikolaja Kopernika/Nicolaus Copernicus University, 2005-06-01)
In this paper, we study positive periodic solutions to singular second order differential systems. It is proved that such a problem has at least two positive periodic solutions. The proof relies on a nonlinear alternative ...
Compression–expansion fixed point theorem in two norms and applications
(Elsevier BV, 2005-09-01)