This is the 8905th most frequent Russian word.
протасевичу
The term "протасевичу" is a form of the surname "Протасевич" in Russian, in the dative case, meaning "to/for Protasevich." It refers to addressing or attributing something to a person with this surname.
In this sentence, Протасевичу is the dative case of the last name Протасевич, used to indicate the recipient of an action.
Я передал документы Протасевичу.
I handed the documents to Protasevich.
Here, Протасевичу again appears in the dative case to show who is receiving the expression of gratitude.
Мы выразили благодарность Протасевичу за помощь.
We expressed gratitude to Protasevich for the help.
The preposition 'по' requires the dative case in this sentence, resulting in Протасевичу to indicate the person mentioned.