RT Journal Article T1 First order differential systems with a nonlinear boundary condition via the method of solution-regions A1 Frigon, Marlène A1 Tella Álvarez, Marcos A1 Fernández Tojo, Fernando Adrián K1 Solution regions K1 Nonlinear boundary conditions K1 Existence results K1 Upper and lower solutions AB In this article we extend the known theory of solution regions to encompass nonlinear boundary conditions. We both provide results for new boundary conditions and recover some known results for the linear case PB Springer Nature YR 2021 FD 2021 LK http://hdl.handle.net/10347/24677 UL http://hdl.handle.net/10347/24677 LA eng NO Frigon, M., Tella, M. & F. Tojo, F.A. First order differential systems with a nonlinear boundary condition via the method of solution-regions. Bound Value Probl 2021, 19 (2021). https://doi.org/10.1186/s13661-021-01495-9 NO This work was partially supported by NSERC Canada. Marcos Tella and F. Adrián F. Tojo were partially supported by Ministerio de Economía y Competitividad, Spain, and FEDER, project MTM2013-43014-P, and by the Agencia Estatal de Investigación (AEI) of Spain under grant MTM2016-75140-P, co-financed by the European Community fund FEDER DS Minerva RD 18 abr 2026