Khmelnitskii, N. A. “Cockcroft–Swan Theorem for Projective Crossed Chain Complexes”. Ukrains’kyi Matematychnyi Zhurnal 66, no. 12 (December 25, 2014): 1694-1704. Accessed April 19, 2024. https://umj.imath.kiev.ua/index.php/umj/article/view/2255.