Molivdovul na Nikola, imperatorski protospatarij i strateg na Mesemvrija, nameren pri archeologičeskite razkopki v Silistra. (Nikola's lead seal, emperor's protospatarii and Messembria's strategist, found during the archaeological excavations in the town of Silistra) - Penčev, Vladimir (Izvestija na Regionalen Istoričeski Muzej Veliko Tărnovo, 20 (2005), 2005)