@article{MO_2020_94_2_a1,
     author = {N. S. Astapov and I. S. Astapov},
     title = {The modern generalizations of the {Ptolemy's} theorem},
     journal = {Matemati\v{c}eskoe obrazovanie},
     pages = {18--28},
     publisher = {mathdoc},
     volume = {94},
     number = {2},
     year = {2020},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/MO_2020_94_2_a1/}
}