Miczko, A., and B. Palczewski. “Some Generalization of Certain O. Hadžić Contraction Type-Theorems”.
Anal. Numér. Théor. Approx.
, vol. 12, no. 2, Aug. 1983, pp. 167-74,
https://ictp.acad.ro/jnaat/journal/article/view/1983-vol12-no2-art8
.