Blömer, J., Brauer, S., &; Bujna, K. (2016). A Theoretical Analysis of the Fuzzy K-Means Problem. In 2016 IEEE 16th International Conference on Data Mining (ICDM) (pp. 805–810). Barcelona, Spain: IEEE.https://doi.org/10.1109/icdm.2016.0094 

Ackermann, M. R., Blömer, J., &; Sohler, C. (2010). Clustering for Metric and Nonmetric Distance Measures. ACM Trans. Algorithms, (4), 59:1--59:26.https://doi.org/10.1145/1824777.1824779