Grigory Gelbak. Elementary Calculation of the Side of the Ninth Tangle. P.P. Soikin. 1925. In Russian (ask us if in doubt)/Grigoriy Gel'bak. Elementarneyshee vychislenie storony devyatiugol'nika. Izd. P.P. Soykina. 1925 g. - landofmagazines.com

TransliterationGrigory Gelbak. Elementary Calculation of the Side of the Ninth Tangle. P.P. Soikin. 1925. In Russian (ask us if in doubt)

In EnglishGrigoriy Gel'bak. Elementarneyshee vychislenie storony devyatiugol'nika. Izd. P.P. Soykina. 1925 g.

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