Gafurova, P.O., Elizarov, A.M. and Lipachev, E.K. 2021. Algorithms for Formation of Metadata Mathematical Retro Collections Based on Analysis of Structural Features of Documents. Russian Digital Libraries Journal. 24, 2 (Apr. 2021), 238-271. DOI:https://doi.org/10.26907/1562-5419-2021-24-2-238-270.