אבן העזר ק״עEven HaEzer 170

Se’if 1א׳

הַיְבָמָה שֶׁנָּתַן לָהּ הַיָּבָם גֵּט כְּרִיתֻת, פְּסָלָהּ וּפָסַל צָרוֹתֶיהָ עָלָיו וְעַל שְׁאָר הָאַחִים, מִדִּבְרֵיהֶם. וְכָל גֵּט שֶׁפּוֹסֵל אִשְׁתּוֹ מְהַכְּהֻנָּה, פּוֹסֵל יְבִמְתּוֹ מֵהַיִּבּוּם; וְאֵינָהּ מֻתֶּרֶת לְזָר, עַד שֶׁיַּחֲלֹץ לָהּ:

A yevama (widow waiting for yibum [a levirate marriage to be performed]) who has received a bill of divorce from the yavam (brother of deceased who must perform levirate marriage), is forbidden on a Rabbinic level from wedding her yavam, and [receipt of this bill of divorce] invalidates her co-wives to the yavam and to the other brothers on a Rabbinic level. All bills of divorce which would invalidate a man's wife from marrying a priest [i.e. the document constitutes a valid divorce], also invalidates a yavama from the performance of yibum [if given to her by the yavam]. And the yavama is not permitted to marry a zar (a non-brother) until the yavam performs chalizta (the ceremony thereby permitting her to marry a non-brother).

Se’if 2ב׳

וְכֵן הַמַּאֲמָר (פי', יְבָמָה נִקְנֵית מִדְּאוֹרָיְתָא בְּבִיאָה, לֹא זוּלַת, וַחֲכָמִים תִּקְנוּ שֶׁיְּקַדְּשֶׁנָּהּ תְּחִלָּה, וְזֶהוּ הַנִּקְרָא מַאֲמָר, פֵּרוּשׁ מַאֲמַר חֲכָמִים), אֵינוֹ קוֹנֶה בָּהּ קִנְיָן גָּמוּר; שֶׁאִם בָּא לְהוֹצִיאָהּ אַחַר הַמַּאֲמָר, צְרִיכָה גֵּט לַמַּאֲמָר, וַחֲלִיצָה לְהַפְקִיעַ הַזִּקָּה:

So, too, statement (an explanation: a sister-in-law is acquired, by Torah [law], through intercourse, nothing else, but the sages amended that he must betroth her first, and this is called "statement", the explanation [of which is] "the sages' statement") does not acquire in her a complete acquisition: for if he wishes to divorce her after the statement she needs [both] a bill [of divorce] for the statement and chalitsah to release the connection.

Se’if 3ג׳

מֵאַחַר שֶׁאֵין מַאֲמָר קוֹנֶה קִנְיָן גָּמוּר, וְלֹא גֵּט דּוֹחֶה דְּחִיָּה גְּמוּרָה, לְפִיכָךְ, מוֹעִיל הַמַּעֲשֶׂה שֶׁנַּעֲשָׂה אַחַר כָּךְ, הֵן גֵּט אַחַר גֵּט, הֵן מַאֲמָר אַחַר מַאֲמָר, אוֹ גֵּט וַחֲלִיצָה וּבִיאָה אַחַר הַמַּאֲמָר, אוֹ מַאֲמָר וּבִיאָה וַחֲלִיצָה אַחַר גֵּט, בֵּין בְּיָבָם אֶחָד וּשְׁתֵּי יְבָמוֹת, בֵּין בִּיבָמָה אַחַת וּשְׁנֵי יְבָמִים, בֵּין בִּשְׁתֵּי יְבָמוֹת וּשְׁנֵי יְבָמִים:

Since statement doesn't acquire a complete acquisition, and a bill [of divorce] doesn't divorce a complete divorce, therefore the action done thereafter works -- whether bill [of divorce] after bill [of divorce]; or whether statement after statement; or bill [of divorce] or chalitsah or intercourse after statement; or statement or intercourse or chalitsah after a bill [of divorce] -- whether with one brother-in-law and two sisters-in-law, or with one sister-in-law and two brothers-in-law, or with two sisters-in-law and two brothers-in-law.