Come and hear: R. Eliezer said to them: If defiled seeds are rendered clean by being sown in the soil, how much more so if [already] sown and rooted [in the soil]! This proves that they do not take effect at all. Now, do not the Rabbis admit the validity of [such] an ad majus conclusion? Surely it was taught: I might think that a man can sell his daughter when a na'arah: — But you can argue a minori: if she who was already sold goes free, is it not logical that if not sold yet, she cannot be sold [now]!