Ekaterina A. Mishina. The interaction between negation and aspect in Old Russian
RJANO. 2020. № 1 (39), Pages. 109 - 135

M. V. Gashneva. The Past Imperfect tense in the bylinas of North Russia and the narrative tradition of Old Russian chronicles
RJANO. 2012. № 1 (23), Pages. 179 - 193