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"Великий князь". Энциклопедический словарь Брокгауза и Ефрона (in Russian). Vol....
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"Великий князь". Энциклопедический словарь Брокгауза и Ефрона (in Russian). Vol. Va. 1892. pp. 754–756. English citation: "Grand Prince". Brockhaus and Efron Encyclopedic Dictionary (in Russian).