Castillo, Alvarado F. L., J. Lawrynowicz, and O. Suzuki. 2008. “Basic Properties and Applications of Graded Fractal Bundles Related to Clifford Structures: An Introduction”. Ukrains’kyi Matematychnyi Zhurnal 60 (5), 603–618. https://umj.imath.kiev.ua/index.php/umj/article/view/3179.