RAO, K.P.R.; KISHORE, G.N.V.; VAN LUONG, Nguyen. A unique common coupled fixed point theorem for four maps under ψ - φ contractive condition in partial metric spaces. CUBO, A Mathematical Journal, [S. l.], v. 14, n. 3, p. 115–127, 2012. DOI: 10.4067/S0719-06462012000300008. Disponível em: https://cubo.ufro.cl/index.php/cubo/article/view/1335. Acesso em: 12 oct. 2025.