1. The Gemara explains why an Onen is allowed to eat the Korban Pesach.
2. There is a dispute about whether a person who converts on Erev Pesach may bring a Korban Pesach.
3. Rava: Sometimes the Rabanan enforced their decrees even when it will cause a person to transgress a Torah Mitzvah.
4. Rava discusses other situations in which the Rabanan enforced their decrees despite negating a Torah Mitzvah.
5. There is a dispute about a person who has a Korban Pesach slaughtered for him while he is too far away to do it himself.
A BIT MORE
1. According to Torah law, the status of an Onen applies only during the day. Even though the Rabanan extended the status of Onen until the deceased relative is buried, they did not enforce this decree when it prevent the Onen from bringing the Korban Pesach (which is punishable by Kares).
2. Beis Shamai: He may. Beis Hillel: The Rabanan decreed that a convert is Tamei for seven days as if he had contact with a corpse.
3. Beis Hillel's ruling in the case above (#2) is an example of such a case. In contrast, in the first case above (#1), the Rabanan did not enforce their decree of Onen when it would prevent someone from bringing the Korban Pesach.
4. For example, if there is no knife available to perform a Bris that is supposed to be on Shabbos, it is forbidden to transgress even an Isur d'Rabanan of Hotza'ah (carrying from one domain to another) in order to carry the knife to perform the Bris.
5. The Torah says that someone who is far away from the Beis ha'Mikdash is exempt from bringing a Korban Pesach. If people slaughter a Korban for him anyway, according to Rav Nachman he fulfills his obligation, while according to Rav Sheshes he does not.