Żołądek, H. “Classification of Diffeomorphisms of $\mathbb S^4$ Induced by Queternionic Riccati Equations With Periodic Coefficients”. Topological Methods in Nonlinear Analysis, vol. 33, no. 2, June 2009, pp. 205-1, https://apcz.umk.pl/TMNA/article/view/TMNA.2009.014.