Balibrea, Francisco, Jose S. Cánovas Peña, and Víctor Jiménez López. “Some Invariants for σ-Permutation Maps”. Annales Mathematicae Silesianae 13 (September 30, 1999): 51–60. Accessed May 6, 2025. https://trrest.vot.pl/ojsus/index.php/AMSIL/article/view/14136.