imperfective aspect
V.S. Xrakovskij. Two verb pairs: radovat’ ‘make happy’(IPFV) and radovat’s’a ‘be happy’ (IPFV), obradovat’ ‘make happy’(PFV) and obradovat’s’a ‘get happy’ (PFV) Meaning and Syntax
Trudy IRY RAS. 2020. № 3 (25), Pages. 115 - 130