οὐ μὴν ἀλλά
From LSJ
τὸ γὰρ μυστήριον ἤδη ἐνεργεῖται τῆς ἀνομίας· μόνον ὁ κατέχων ἄρτι ἕως ἐκ μέσου γένηται. (2Thess 2:7) → For the mystery of lawlessness is already at work — just at work until the one who is now constraining it is taken out.
English (LSJ)
A nevertheless, notwithstanding, yet, still, ἀληθῆ μέν ἐστι τὰ πολλά, οὐ μὴν ἀλλ' ἴσως οὐχ ἡδέ' ἀκούειν D.4.38, cf. 1.4, 2.22; so οὐ μὴν ἀλλά… γε, Pl.Grg. 449b, Plt.263b.
II οὐ μὴν ἀλλὰ καί... not only so, but what is more, D.37.23, S.E.M.5.99.