Yerushalmi Yevamot 4:9 ירושלמי יבמות ד׳:ט׳

MISHNAH: If somebody performs ḥalîṣah with his sister-in-law while his brother had married her sister and then died, she must perform ḥalîṣah but not levirate¹²³She is prohibited to the levir by Mishnah 8. But these prohibitions are rabbinical. Since by biblical standards she could have been married in levirate, she needs ḥalîṣah.. Similarly, if somebody divorces his wife while his brother had married her sister and then died, she is free¹²⁴The widow of the brother is forbidden to the levir by biblical standards, there can be no levirate and, therefore, no ḥalîṣah..

HALAKHAH: “Similarly, if somebody divorces his wife,” etc. ¹²⁵Chapter 1, Notes 90, 91. Simeon bar Abba asked before Rebbi Joḥanan: What is the difference between having ḥalîṣah and divorcing⁹⁰In the Babli, 38b, this is quoted as the opinion of Abbai (middle 4th Cent.), with a belated acknowledgment (39a) of the priority of R. Yose ben Ḥanina (middle 3rd Cent.). As Levy Ginzburg has pointed out, in the Babylonian Talmud the Babylonian authors are always mentioned before the Galileans; chronological order is followed within each group separately.
The wife of a childless man who has a brother becomes “a woman waiting for her levir” at the moment she is widowed.? He said to him: You think that ḥalîṣah is acquisiton, but it is only freeing. The brothers are not guilty⁹¹This opinion is not mentioned in the Babli. There, the opinion opposed to that of Abbai is that of Rava, who holds that the widow can only dispose of her property before “bespeaking”. For him, “bespeaking” for the House of Shammai makes the widow a wife in civil but not in criminal matters, while qiddushin makes the unencumbered woman a wife in criminal but not in civil matters. for her under the category of “wife of the one acting in ḥalîṣah” but they are guilty under the category of “wife of the deceased”.