@article{VMUMM_1987_5_a3,
     author = {V. I. Ponomarev and V. V. Tkachuk},
     title = {The countable character of $X$ in $\beta X$ versus the countable character of the diagonal in $X\times X$},
     journal = {Vestnik Moskovskogo universiteta. Matematika, mehanika},
     pages = {16--19},
     year = {1987},
     number = {5},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/VMUMM_1987_5_a3/}
}