PODLIPENKO, Yu. K. Boundary-value problems for Helmholtz equations in an angular domain. I. Ukrains’kyi Matematychnyi Zhurnal, [S. l.], v. 45, n. 3, p. 403–418, 1993. Disponível em: https://umj.imath.kiev.ua/index.php/umj/article/view/5823. Acesso em: 6 dec. 2025.