A yevama (widow subject to levirate marriage) goes [to court] according to the place of the yavam (living brother of her husband), and the court advises them appropriately, whether to consummate levirate marriage or to undergo chalitza (ceremony to break levirate bond). Rama: This rule applies when the yavam is in his place of residence, and there is a court in town. But if he has traveled elsewhere, we do not force the widow to go after him (Nimukei Yosef, end of chapter Zeh Borer - Sanhedrin). Similarly if he lives among Kuthites (non-Jews) or non-educated [Jews] who do not know the rules of chalitza, the judges are not required to go after him, but can force him to come to the place of assembly (court) and he frees his yevama (Hagahot Alfasi chapter Mitzvat Chalitza - Yevamot).
According to the Torah, he doesn't need to marry her, rather "come unto her" (have relations). And the Rabbis decreed that he shouldn't "come unto her" until he marries her in front of witnesses, with money or document, and that's called Ma'amar. Ram"a: And if he marries her with a document, that's also called Ma'amar. And even if he gave to her a peruta and says to her, "Behold you are married to me with this and with my brother's marriage," behold [she] is married, since it's like a loan and a peruta (Riva"sh Siman 162). And she also needs the wedding canopy after the marriage, like 0ther woman. And he can do Ma'amar through an agent, like other marriages (ad loc Siman 1). And if he comes unto her without Ma'amar, he acquires her, and he doesn't have to redo and marry her, and we whip him rebellious lashes. Ram"a: And specifically when he comes unto her in front of witnesses.
We don't do Ma'amar with except with her consent. And a minor that was widowed from bethrotal, we only do Ma'amar with her with the consent of her father.
He writes her a ketubah, but the yavam's possessions are not mortgaged to her, because her ketubah are on her first husband. And if her first husband did not have possessions, her ketubah is on the yavam.
A son is born from him, but the son does not need to be called the name of the brother who died [the first husband].
One who has relations with his yevama, whether by accident or for promiscuity, whether Kutim forced him onto his yevama against his will when he was hard, whether he did it on purpose and she by mistake or forced, whether she did it on purpose and he mistakenly or forced, whether she was awake or asleep, he acquired [married] her, even if they only started it.
What are the circumstances [above, that intercourse without intention to effect levirate marriage still do effect levirate marriage]? When he intended to have intercourse, even if he intended bestiality [but instead had intercourse with the yevama]. But if he did not intend to have intercourse at all, as when he was asleep or so drunk that he does not recognize his surroundings, or he intended to ejaculate on the wall and he instead ejaculated into the yevama, or he became erect for his wife, and then fell from the roof and impacted on the yevama, then he does not acquire the yevama. Similarly, if others inserted him into the yevama without erection, but with a soft member, he does not acquire.
what is the source that negligent relations is an engagement? In Yevamot [in the case] that she fell to him for Marriage. But If she fell to him for the engagement, there are those that say this is not an acquiring [and does not give her legal status] to be a heir and she is impure and her marital vow is broken, there are those that say that this is the rule with relations out of wedlock. There are those that say that the one who comes to have relations needs to say the benediction: "Who has sanctified His commandments and commanded us about [relations] with a Yevamah"