Gemara

(Beraisa): If the bread was baked, the animals were slaughtered, or the wine was mixed, and then the Chasan's father or bride's mother died:

We put the deceased in a room until after the Chupah...

All 14 days he sleeps among men, and she sleeps among women.

4a: This supports R. Yochanan, who says that even though we do not show signs of Aveilus during the Mo'ed (the seven days of nuptial festivities are like a Mo'ed), private matters (relations) are forbidden.

4b: We are stringent to make them sleep separate among men/women because we were lenient about the Aveilus.

The leniency is not that we allow relations before the burial. Aveilus did not begin yet!

Rather, we were lenient to postpone Aveilus until after the seven days of festivities.

Mo'ed Katan 23b - Suggestion: Tana'im argue about whether or not Aninus applies on Shabbos.

(Beraisa): If one's Mes is in front of him, on Shabbos he reclines, and eats meat and wine. He blesses before and after eating and joins a Zimun. He is obligated in all Mitzvos;

R. Gamliel says, because he is obligated in these, he is obligated in all Mitzvos.

(R. Yochanan): R. Gamliel and Chachamim argue about marital relations.

Suggestion: Chachamim hold that Aveilus applies on Shabbos, and R. Gamliel disagrees.

Rejection #1: All say that Aveilus does not apply on Shabbos. Chachamim exempt an Onen from relations because the Mes is in front of him.

Rejection #2: All say that Aveilus applies on Shabbos. R. Gamliel obligates an Onen because Aveilus did not start yet.

Rishonim

The Rif (Berachos 10b) brings our Gemara.

R. Yonah (DH uv'Shabbos): He must fulfill Mitzvos. Eating meat and wine on Shabbos is not obligatory. It is better to forego them than to take money from others.

R. Yonah (DH Tashmish): The first Tana forbids relations because it is lightheadedness for one whose Mes is in front of him. R. Gamliel obligates, but he should not do so for pleasure above the Mitzvah of Onah. The Rif rules like the Rabim (Chachamim).

Question: If so, why does it say (Kesuvos 4b) that allowing Bi'as Mitzvah is not a leniency, because Aveilus did not begin yet? The Isur Bi'ah of Aveilus applies even during Aninus!

Answer (R. Yonah): Bi'ah during Aveilus is a proper Isur. During Aninus we are stringent because it is lightheadedness; we are not stringent regarding Bi'as Mitzvah.

R. Yonah (DH veha'Rav): R. Yosef ha'Levi says that the Tana'im argue about whether or not Mitzvas Onah is obligatory for an Onen, but all permit. However, the Yerushalmi clearly holds that Chachamim forbid.

R. Yonah (DH Aval): The Yerushalmi explicitly rules like R. Gamliel. The Bavli did not need to say so, for it gave a Kelal that the Halachah follows the lenient opinion in Aveilus. Even though Aveilus begins after burial, the Isur during Aninus is due to the Isur during Aveilus, therefore the Kelal applies.

Rebuttal (Rosh 3:2): BaHaG rules like Chachamim, who forbid. We do not apply the rule that the Halachah follows the lenient opinion in Aveilus, because Aveilus does not apply before burial. If the Bavli held like R. (Shimon ben) Gamliel, it would have said so.

R. Yonah (ibid.): Aninus does not apply on Shabbos or Yom Tov. The Yerushalmi exempts an Onen from Shofar. Perhaps it does not argue with the Bavli; it exempts only at the end of the day, when he can be Machshich Al ha'Techum (go as far from the city as is permitted, to hasten obtaining needs of burial after dark). The same applies to Shabbos. The Ramban was an Onen on Rosh Hashanah, and asked people to be Motzi him in Shofar.

Rosh (Berachos 3:1, 3:3 and Mo'ed Katan 3:54): Aninus applies on Yom Tov, because one may command Nochrim and transgress Shevus for the sake of burial. Burial is never permitted on Shabbos, so Aninus does not apply. Some say that on both Shabbos and Yom Tov Aninus applies only at the end of the day, when he can be Machshich Al ha'Techum. However, if the Mes is in the Reshus of a governor who does not allow burial, the relatives cannot do anything for burial, so even this opinion would permit relations.

Rambam (Hilchos Evel 4:6): If one's Mes is in front of him, on Shabbos he reclines, eats meat and wine, blesses before and after eating, and joins a Zimun. He is obligated in all Mitzvos except for relations.

Mishneh l'Melech: The Manhir (73) says that all Mitzvos of the Seder apply to an Onen on Pesach. However, the Hagadah expounds verses at length, so it is better that he hear it from another. It seems that this is even on the second night. An Onen is exempt from Mitzvos only during the day, but not at night.

Hagahos Maimoniyos (5): Aninus does not apply on Shabbos, Yom Tov or Chol ha'Mo'ed, except for private matters. Kri'as ha'Torah is considered a private matter, unless he normally receives a particular Aliyah, e.g. Kohen or the last Aliyah. If he is the only Kohen in the Beis ha'Keneses he should be called to read, for otherwise it looks like public Aveilus. It is better that he leave before Kri'as ha'Torah. SMaK learns from the Yerushalmi that there is Aninus on Chol ha'Mo'ed. However, it seems that the Bavli disagrees.

Poskim

Shulchan Aruch (YD 341:1): If one lost a relative for whom Aveilus applies, before burial he eats in a different house. If he cannot, he makes a Mechitzah and eats. If he cannot, he faces away from the Mes and eats.

Shach (3): Eating in front of one's Mes is like mocking the dead. This applies even on Shabbos.

Shulchan Aruch (ibid.): On Shabbos he eats meat and wine (Rema - if he wants), blesses and is obligated in all Mitzvos except for relations, which is forbidden.

Shach (7): The Rema rules like R. Yonah, who says that eating meat and wine on Shabbos is optional. Blessing is obligatory.

Beis Yosef (DH v'Dikdek): In the Yerushalmi Tana'im argue about whether or not relations are forbidden. The Rif, Rambam and Rosh all forbid.

Rebuttal (Bach DH u'Mah she'Chosav v'Chosav): The Rambam (Evel 1:2) says that Isurei Aveilus do not apply to an Onen. The Ramban (brought in the Tur) disagrees. He says that all forbid relations to an Onen during the week. The Rambam holds like R. Yosef ha'Levi (brought in R. Yonah above), that the Tana'im argue about whether or not Onah is obligatory for an Avel on Shabbos, but all permit relations even during the week.

Shulchan Aruch (ibid.): However, if he needs to be Machshich Al ha'Techum to prepare needs of burial, Aninus applies from when he goes. If he plans to bury the Mes on Yom Tov Rishon through Nochrim, all Isurei Aninus apply. All the more so they apply if he will bury it on Yom Tov Sheni, when he himself can bury it.

Taz (3): The Maharshal permitted an Avel to make Kidush on the night of Yom Tov Sheni because Aninus does not apply on Yom Tov. It seems that this is only at night, for normally we do not bury at night.

Shach (9): The Maharshal holds like the Poskim who says that Aninus does not apply at all on Yom Tov Sheni. We hold like the Rosh, that it applies, i.e. even at night.

Mishnah Berurah (71:11): We exempt from Aninus on Yom Tov night because normally we do not bury at night. On a weekday, Aninus applies also at night.

Magen Avraham (548:8): Nowadays our custom is to bury through Nochrim even on Yom Tov Sheni, so all the more so Aninus does not apply at night.

Shulchan Aruch (OC 71:2): On Shabbos an Onen is obligated to read Shma the entire day until evening.

Mishnah Berurah (10): The Taz (4) says that even though the time for Shma is after dark, he should read earlier at the end of Shabbos, while he is still obligated. Others disagree. One should read then, without the Berachos.

Kaf ha'Chayim (13): The Shevus Yakov says that one may not pray Ma'ariv and say Havdalah before night, for once he says that it is Chol, Aninus applies, and he may not pray. The Machatzis ha'Shekel disagrees. It is not Kedushas Shabbos that exempts from Aninus, rather, the inability to engage in burial, and this is until night.

Shulchan Aruch (ibid.): If he is Machshich Al ha'Techum to hasten obtaining needs of burial after dark, he ceases to be obligated when he goes.

Beis Yosef (DH u'Mah she'Chosav v'Afilu): During the week Aninus applies even if others do the needs of burial, in order that the Onen will be free to think about the needs of the Mes constantly. On Shabbos he cannot do more for the Mes than to be Machshich, therefore Aninus applies only at that time.

Beis Yosef (DH u'Mah she'Chosav dev'Shabbos): The Tur exempts shortly before dark because one can be Machshich. This is after the time for morning Shma, and the time for evening Shma is not until Tzeis ha'Kochavim, and Shabbos is over then! His words here pertains to Chiyuv in other Mitzvos.

Magen Avraham (3): Perhaps the Tur alludes to our custom to read Shma and pray Ma'ariv before evening.

Kaf ha'Chayim (13): The Drishah says that if there is a need to be Machshich for this Mes, i.e. there are needs unavailable in this city, the Onen is exempt even if he is not Machshich.

Shulchan Aruch (ibid.): Yom Tov Sheni is like a weekday. Yom Tov Rishon is like Chol if he plans to bury that day through Nochrim. If not, it is like Shabbos.

Shulchan Aruch (548:5) Yom Tov Sheni is like Chol only if he will bury that day.

Mishnah Berurah (20): It depends on whether or not he could bury that day, not on his intent.

Dagul me'Revavah (DH Lo): The Magen Avraham (8) forbids Divrei Torah to an Onen during the Regel because it gives Simchah. I disagree. Aninus does not apply on Shabbos and Yom Tov. R. Gamliel and Chachamim argued about relations. They did not argue about Divrei Torah, for all permit!

Kaf ha'Chayim (21): When Aninus does not apply, he is obligated in Simchah and to drink wine. He may not be stringent.