αὐτὸν κέκρουκας τὸν βατῆρα τοῦ λόγου → you have struck the very threshold of the argument, you have struck the most important and chiefmost point
destechar τὴν ὀροφήν Iust.Phil.Qu.et Resp.M.6.1277B, cf. en v. pas. ib.
