Reference for Sanhedrin 115:12

רע"א אביו אשת אביו ואימא אביו ממש היינו ודבק ולא בזכר א"ה אשת אביו נמי היינו באשתו ולא באשת חברו לאחר מיתה

and they shall be as one flesh, applying to those that can become one flesh, thus excluding cattle and beasts, which cannot become one flesh with man.<span class="x" onmousemove="('comment',' Hence R. Meir's dictum that heathens are forbidden those relations which are prohibited to Jews on pain of death, e.g., the father's wife, reflects R. Akiba's teaching, whilst his ruling in the Baraitha that a proselyte may marry his father's wife is R. Eliezer's view, who does not interpret 'his father' as his father's wife. ');">¹²</span>

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