XU, Z.; XING, H. Integral operator and oscillation of second order elliptic equations. Tamkang Journal of Mathematics, [S. l.], v. 36, n. 2, p. 93–101, 2005. DOI: 10.5556/j.tkjm.36.2005.121. Disponível em: https://journals.math.tku.edu.tw/index.php/TKJM/article/view/121. Acesso em: 26 apr. 2024.