RT Journal Article T1 Reflection equation with piecewise constant arguments A1 Cabada Fernández, Alberto A1 Cambeses Franco, Paula K1 Green’s function K1 Equation with reflection K1 Piecewise constant arguments K1 Constant sign solutions K1 Nonlinear problem K1 Monotone method K1 Nonlocal problems AB In this work, we study nonlocal differential equations with particular focus on those with reflection in their argument and piecewise constant dependence. The approach entails deriving the explicit expression of the solution to the linear problem by constructing the corresponding Green's function, as well as developing a novel formula to delineate the set of parameters involved in the analyzed equations for which the Green's function exhibits a constant sign. Furthermore, we demonstrate the existence of solutions for nonlinear problems through the utilisation of diverse results derived from fixed-point theory.The aforementioned methodology is specifically applied to the linear problem with periodic conditions $v'(t) + mv(-t) + Mv([t]) = h(t)$ for $t \in [-T,T]$, proving several existence results for the associated nonlinear problem and precisely delimiting the region where the Green's function $H_{m,M}$ has a constant sign. % when $T \in (0,1]$.The equations studied have the potential to be applied in fields such as biomedicine or quantum mechanics. Furthermore, this work represents a significant advance, as it is the first time that equations with involution and piecewise constant arguments have been studied together. PB Elsevier SN 1878-7274 YR 2026 FD 2026-02-01 LK https://hdl.handle.net/10347/44902 UL https://hdl.handle.net/10347/44902 LA eng NO Commun Nonlinear Sci Numer Simulat 153 (2026) 109488 NO The authors were partially supported by Grant PID2020-113275GB-I00, funded by MCIN/AEI/10.13039/501100011033 and by “ERDF A way of making Europe” of the “European Union”, and by Xunta de Galicia (Spain), project ED431C 2023/12. The second author would like to express her gratitude to the Spanish Ministry of Science, Innovation and Universities for financial support (Grant reference FPU 23/02202). DS Minerva RD 26 abr 2026