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Ἓν οἶδα, ὅτι οὐδὲν οἶδα → I know only one thing, that I know nothing | all I know is that I know nothing.
κρύβδᾱν prep. c. gen., 1 without the knowledge of ἄλλον αἴνησεν γάμον κρύβδαν πατρός (P. 3.13)