Golasinski, M., D. Goncalves, and P. Wong. 2005. “Generalizations of Fox Homotopy Groups, Whitehead Products, and Gottlieb Groups”. Ukrains’kyi Matematychnyi Zhurnal 57 (3), 320–328. https://umj.imath.kiev.ua/index.php/umj/article/view/3600.