Examples: cartography card archaeology archetype monarchy legal loyal purse personal cinema kinase car carpenter hippopotamus Mesopotamia dative data date
...
Old East Slavic сѧ

→ Belarusian -ся (inherited)
→ Belarusian вучыцца (mention)
→ Russian -ся (inherited)
→ Russian учиться (mention)
→ Ukrainian -ся (inherited)