La Rosa, Vincenzo, and Pasquale Vetro. “On Fixed Points for for alpha–eta–psi-Contractive Multi-Valued Mappings in Partial Metric Spaces”. Nonlinear Analysis: Modelling and Control, vol. 20, no. 3, July 2015, pp. 377-94, https://doi.org/10.15388/NA.2015.3.5.