Parsha Chanura Tzav/Pesach: Inyanei Afikomin

This week's chaburah was taken from a few pieces found in Harirei Kedem by Rav Shirkin. For those who don't know, Rav Shirkin was a talmid of Rav Soloveirchik and the sefer Harirei Kedem is a selection of pieces that he heard from Rav Soloveitchik on the Moadim.

The gemara in Pesachim (119B) says that "ain maftirin acher hapesach afikomon" which loosley translated means "don't eat anything after the Korbon Pesach". The same halacha is mentioned regarding the matzah we eat at the end of the seder.

The question is what is the reason for this halacha.

Shittas Rashbam/Rosh

You have to eat the korbon pesach when you are full. If we allow you to eat after the korbon pesach there is a concern that you will eat the korbon pesach on an empty stomach and eat the rest of the meal afterwards. Therefore, a taknah was made that you can't eat after the korban pesach and this will ensure you are full when you eat the korbon.
B'zman hazeh, we eat the afikomon matzah as a zecher to what they did when they had a korbon pesach.
There is one difference between the Rosh and the Rashbam. The Rashbam holds that b'zman hazeh the matzah we eat is a zecher to the matzah that was eaten with the korbon and the Rosh holds it is azecher to the korbon that was eaten. (Nafka mina is whether the afikomon matzah is the ikkar mitzvah of matzah).

Shittas Tosfos/Rambam

Tosfos and the Rambam seem to understand the reason is so that the taste of the matzah/korbon will last. The Rambam seems to learn that it is a din in the achilas hamatzah. Since eating the matzah is a mitzvah we want the taste of the matzah to last the night.
Rav Shirkin actually brings down a Brisker Rav that this yesod should apply to all mitzvas achilah. Howeevr, Rav Shirkin then tries to prove it is only a special inyan for matzah and korbon pesach.

There is also a Ba'al HaMeor and Milchamos on this. ayin sham.

Nafka Mina

1) If one eats after the afikomon does one need to eat the afikomon again?

Rashbam/Rosh: No. It is only an issur/gezeirah in the first place so if you were oveir the gezeirah what can you do.
Rambam/Tosfos: Yes. You need to have ta'am matzah in your mouth.

2) Can one eat just one piece of matzah the whole night by motzi matzah and nothing else or do you need to eat a piece at the end of the seder also.

Rashbam/Rosh: No. Since the gezeirah is so you eat the korbon when full, you would need to be full when you eatthe afikomon. When you eat the first piece of matzah you ate it on an empty stomach so you would have to eat again.

Rambam/Tosfos: Yes. As long as you have ta'am matzah in your mouth it is sufficient

3) Tenai of the Avnei Nezer: If one has not eaten the afikomon by chatzos the Avnei Nezer says eat the afikomon with a tenai, finish your meal and eat another piece of matzah. The tenai is if the halacha is like R' Eliezer Ben Azaria and the mitzva is until chatzos so this piece is teh afikomon. If we pasken that you have until alos hashachar so this piece is not the afikomon and the last piece you eat after the meal is the afikomon.

The question is does this tenai work acc. to the different Rishonim. I will leave this hanging since I am unclear on this part. You can look in the Harirei Kedem to see how he explains it.