1. L. Brailovsky, On (3,m)-special elements in groups, Comm. Algebra (1992), no. 11, 3301–3320.[MR]
  2. Leonid Brailovsky, Dmitrii V. Pasechnik, and Cheryl E. Praeger, Classification of 2-quasi-invariant subsets, Ars Combin. 42 (1996), 65–76.[MR]