AGARWAL, Ravi P.; O’REGAN, Donal. Positive solutions for a class of Volterra integral equations via a fixed point theorem in Fréchet spaces. Topological Methods in Nonlinear Analysis, [S. l.], v. 28, n. 1, p. 189–198, 2006. Disponível em: https://apcz.umk.pl/TMNA/article/view/TMNA.2006.027. Acesso em: 8 jul. 2025.