[andai]

GPT 3.5: No, it is not possible for a man to marry his widow's sister because by definition, a widow is a woman whose spouse has died. If a man is deceased, then he cannot marry anyone, including his widow's sister. This is a logical impossibility and would not be recognized as a valid marriage under any legal system.

Koala: The legality of a man marrying his widow's sister varies by jurisdiction. In some countries, such as the United States, it is generally legal for a man to marry his widow's sister. In other countries, such as the United Kingdom, it is illegal for a man to marry his widow's sister because it is considered incest. It is always important to check the laws and regulations in the jurisdiction in which the marriage will take place to ensure that it is legal.

https://chat.lmsys.org/?model=koala-13b