ἐπιμελεῖσθαι

From LSJ

Πόλις γὰρ οὐκ ἔσθ' ἥτις ἀνδρός ἐσθ' ἑνός → The state which belongs to one man is no state at all

Sophocles, Antigone, 737

Lexicon Thucydideum

curam habere, operam dare, to take pains, devote effort, 3.25.1, 4.2.3, 4.118.3. 6.41.4, [depravati codd. corrupted manuscripts ἐπιμελήμ.] 6.91.5. 7.8.3, 8.68.1.
idem, the same 6.54.6, 7.39.2, [Vat. et alii Vatican and other manuscripts ἐπιμελουμ.].