Opinion#1: Rashi explains that this was because Rebbi held the prohibition of "Lo Saneh Al Riv" -- "Do not answer regarding an argument" (Shemos 23:2, meaning that the judges are not allowed to argue on the greatest judge present) pertained to all cases (even regarding money matters).

Question: This does not seem to be correct, as it is not logical to say that our Gemara is arguing on the Mishnah in Sanhedrin (32a) that it just quoted. (Note: It is possible Tosfos means that Rebbi himself would not have recorded the Mishnah in Sanhedrin without including his dissenting opinion. The fact that he did not add anything indicates he is not arguing (notes on Tosfos ha'Rosh).)

Opinion#2: Rather, Rebbi did this in order not to make himself appear as the greatest person there.

Explanation: Huna Bar Nasan was a Torah scholar and a wealthy man, as is stated in Moed Katan (28a) that Rav Ashi was (indirectly) pushing aside Huna bar Nasan (from being the head Torah scholar, as Rav Ashi had not yet died). The Gemara in Zevachim (19a) states regarding Huna bar Nasan that the Pasuk, "And kings will be your workers," (Yeshayahu 49:23) was fulfilled by him.

Observation: Being that he did not add, "Both a present of movable objects and a present of land" it implies that he was specifically referring to movable objects.

Implied Question: The Gemara in Bava Basra (155b) says regarding someone who is less than twenty years old that he cannot sell his father's possessions, but his present is valid. The Gemara there is discussing land (even though this is not explicitly stated). (Note: This shows that his acquisitions regarding land do work, unlike our Gemara which appeared to relegate this to movable objects.)

Answer: The Gemara there is referring to a person who was thirteen and one day. He merely was not twenty. (Note: When it said, "less than twenty," it did mean to include younger than thirteen (see Korban Nesanel on the Rosh here who gives this explanation of Tosfos).)

Explanation: This is referring to taking Ma'aser Ani or charity if he is poor, or if he is with friends having a meal. However, this does not mean that he can take first when dissolving a partnership.

Proof: This is as the Gemara states in Pesachim (50b) that if someone puts his eyes on the best portion, he does not see a sign of blessing (from endeavors to get that portion).

Observation: Rabeinu Chananel says that this applied in their days, when they were busy working and there were not a lot of people present (it seems they did not make this decree on Monday and Thursday when there were not many people). However, we who do have a lot of people present have the same law on Monday and Thursday as on Yom Tov.

Observation: This implies that if all Kohanim were not subservient to him, it would be forbidden (for a great Yisrael to get the Aliyah in place of a Kohen) even if he would be bigger than all of the people of his city.

Implied Question: The Gemara in Megilah (28a) states that Rebbi Preida says that he never blessed (meaning led a Mezuman) before a Kohen. The Gemara asks a question from a statement that a Chacham who reads after a Kohen who is an ignoramus is liable to be killed (by Hash-m). The Gemara therefore says that Rebbi Preida must not have led the Mezuman before a Kohen as long as the Kohen was equal to him in stature.

However, the Gemara obviously does not mean literally equal, as otherwise it would be obvious the Kohen should lead the Mezuman. Rather, the Gemara's answer means that he would not bless before a Kohen who was not an ignoramus.

Answer#1: We must say that all of the Kohanim were subservient to Rav Preida as well. Otherwise, what is the novelty of this statement?

Answer#2: Alternatively, our Gemara only requires that everyone else be subservient to him on Shabbos and Yom Tov. Rebbi Preida would not even take the Aliyah of Kohen on Monday or Thursday before a learned Kohen (even though he could have done so without them being subservient to him).

Explanation: Rebbi Yitzchak b'Rebbi Yehudah explains that the Levi is called in his regular place (second, see Rashi DH "Nispardah" that there is an argument about the explanation of the Gemara).

Implied Question: The Gemara in Kesuvos (25b) says, "We see this person is a Kohen, as a Levi read the Torah after him." (Note: This implies that we never have a Levi receive an Aliyah unless a Kohen read before him, unlike the explanation above.)

Answer: We must say that it was obvious in Kesuvos that the first person was a Kohen, as the Levi is greater than the person called before him, or smaller than the person called after him. (Note: Being that he is greater, he should have been called up for the first Aliyah if not for the fact that the first person was clearly a Kohen. Similarly, if the Levi would be a Yisrael, he should not be receiving an Aliyah before the person who read after him, who is greater than him in stature.)

Observation: According to the Mishnah in Megilah (21b) that everyone makes a blessing before and after the Aliyah, this is understandable.

Implied Question: The Mishnah there stated that originally the law was that the first one to read the Torah said the opening blessing, and the one to finish reading the Torah recited the blessing after the reading was finished. (Note: If the same Kohen keeps reading the Torah and he did not recite any blessing (as he is one of the middle Aliyos), how would it be clear that there were two Aliyos (Tosfos ha'Rosh)?)

Answer: The case must be where the Kohen read the Torah and sat down in the interim (and then got called to the Torah again).

If the case was different, how would it be clear that there were two different readings? This is like the Tosefta in Megilah that states that if there was only one person present who knew how to read the Torah, he reads, sits down, and then stands up and reads (as many times as there are Aliyos).

The Tosefta is clearly before the decree. After the decree that everyone receiving an Aliyah should make a Berachah before and after their Aliyah, this (sitting and then standing - Tosfos ha'Rosh) is not necessary.

Observation: They write in the name of Rabeinu Yehudah that if there are only Kohanim in a Shul, one Kohen reads instead of seven (Aliyos). He should make a Berachah before and after each Aliyah.