TіmоkhоvіchV. L. “On One Property of Spaces Admitting a Perfect Mapping onto the Metric Ones ”. Ukrains’kyi Matematychnyi Zhurnal, Vol. 23, no. 1, Dec. 1970, pp. 43-48, https://umj.imath.kiev.ua/index.php/umj/article/view/8477.