PĂPARĂ, Nicolae Valentin. Convergence of the Neumann series for a Helmholtz-type equation. Studia Universitatis Babeș-Bolyai Mathematica, [S. l.], v. 61, n. 1, p. 109–116, 2016. Disponível em: https://studia.reviste.ubbcluj.ro/index.php/subbmathematica/article/view/5522. Acesso em: 19 apr. 2025.