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Books about Vyachko:
Sovetskaya istoricheskaya entsiklopediya. Tom 3. VAShINGTON - VYaChKO (2012)
Wiki information Vyachko:
Vyachko of Koknese, also Vetseke of Kokenhusen was the ruler of the Principality of Koknese in present-day Latvia, a vassal of Polotsk, who unsuccessfully tried to establish himself as a local ruler first in Latvia and then in Estonia, and fought...