Maria N. Sheveleva. Once more on the imperfect of perfective verbs in Old Russian texts
RJANO. 2018. № 1 (35), Pages. 183 - 206

Maria N. Sheveleva. Imperfective verbs with the suffix -yva-/-iva- in North Russian chronicles
RJANO. 2013. № 2 (26), Pages. 205 - 240