@article{MO_2000_2_a1,
     author = {N. S. Astapov},
     title = {Theorem on a {Quadrangle}},
     journal = {Matemati\v{c}eskoe obrazovanie},
     pages = {22--28},
     year = {2000},
     number = {2},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/MO_2000_2_a1/}
}