Kalachikova O.N., Korolenko A.V., Bobrova A.G. Demographic development of Russia and Belarus in the 21st century in the context of the introduction of the active longevity concept. Problems of Territory's Development, 2021, vol. 25, no. 1, pp. 29–51. DOI: 10.15838/ptd.2021.1.111.2