MaksimenkoS. I., and FeshchenkoB. G. “Homotopic Properties of the Spaces of Smooth Functions on a 2-Torus”. Ukrains’kyi Matematychnyi Zhurnal, Vol. 66, no. 9, Sept. 2014, pp. 1205–1212, https://umj.imath.kiev.ua/index.php/umj/article/view/2211.