Blömer, Johannes, et al. “A Theoretical Analysis of the Fuzzy K-Means Problem.”10.1109/icdm.2016.0094__2016 IEEE 16th International Conference on Data Mining (ICDM), IEEE, 2016, pp. 805–10, doi:10.1109/icdm.2016.0094.

Ackermann, Marcel R., et al. “Clustering for Metric and Nonmetric Distance Measures.”10.1145/1824777.1824779__ACM Trans. Algorithms, no. 4, 2010, pp. 59:1--59:26, doi:10.1145/1824777.1824779.