2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/67847This paper is concerned with the solvability of some abstract differential equation of type $$\dot u(t) + Au(t) + Bu(t) \ni f(t), t \in (0,T], u(0) = 0,$$ where $A$ is a linear selfadjoint operator and $B$ is a nonlinear(possibly multi-valued)maximal monotone operator in a (real) Hilbert space ${\mathbb H}$ with the normalization $0 \in B (0)$. We use the concept of variational sum introduced by H. Attouch, J.-B. Baillon, and M. Théra, to investigate solutions to the given abstract differential equation. Several applications will be discussed, among them the case where $B = \subdifferential ϕ$, the subdifferential of a convex semicontinuous proper function $ϕ$.10 pagesAnalysis of PDEs47H14; 35B15; 47J35text