פירוש על קידושין 101:11

The mishnah is used as a difficulty against Rava. A man cannot betroth both a woman and her sister, daughter or mother. But if he says to a woman and her mother/sister/daughter, “One of the two of you is betrothed to me” by deduction it would seem that they all could be doubtfully betrothed even though sex with any of them would be prohibited. This seems to be a refutation of Rava.