numismatic literature
auction catalogs
Gorny & Mosch Giessener Münzhandlung, Auktion 136, Sammlung Kruse, Russland, Teil I, München 14/15.10.2004.
1458 items (No. 6001-7458), a catalog of a comprehensive collection of Russian coins among which a very rich collection of Yefimeks, with numerous varieties within each year, an important catalog for any collector of Russian coins