Ma'aser Sheni, Chapter 4, Mishnah 3. This mishnah deals with the question of priority in redemption: when two people compete over the right to redeem ma'aser sheni, to whom is that right granted.
The first case - both offer a sela:
"Ba'al habayis omer b'sela v'acher omer b'sela - ba'al habayis kodem" - the owner, the person who grew the produce or who owned the ma'aser sheni, says that he wishes to redeem the ma'aser for a sela, and another person, who is not the owner, also offers a sela. The halachah gives priority to the owner, and he is the one who takes the sela and brings it up to Jerusalem.
And the reason is: "mipnei shehu mosif chomesh" - the halachah establishes that when the owner of the ma'aser sheni is the one redeeming, he must add a fifth to the redemption money. This addition is a quarter of the original principal, and once it is combined with the principal it turns out to be a fifth of the total sum. This is what is known as "chomesh milbar" - a fifth from the outside, since the calculation is made from the total sum after the addition.
Another person who redeems ma'aser sheni that has no connection to him is not obligated to add a fifth. It emerges that the ma'aser sheni stands to gain from having the original owner redeem it, and for that reason the owner is given priority.
The second case - the other person adds an issar:
"Ba'al habayis omer b'sela v'acher omer b'sela v'issar" - the owner of the ma'aser sheni offers to redeem it for a sela, and another person offers a sela plus an issar. And what is the value of an issar? According to the breakdown of the coins:
A sela consists of four dinars.
Each dinar consists of six ma'ah.
Each ma'ah consists of four issarim.
It emerges that an issar is one ninety-sixth of a sela - a truly minimal addition.
Even so, the mishnah rules: "shel sela v'issar kodem" - the person willing to add this small amount has priority, even though he will not be adding a fifth, which is far greater than that issar. And the reason is: "mipnei shehu mosif al hakeren" - the other person is adding to the principal itself, and an addition to the principal is preferred. The Rishonim explain that the owner can always extricate himself from the obligation to pay the fifth, as we will see in the next mishnah, and since there is a way to bypass the obligation, we do not rely on his addition of a fifth. Therefore, whoever adds to the principal has priority, even if his addition to the principal is less than the fifth.
"Hapodeh ma'aser sheni shelo - mosif chomesh":
The mishnah goes on to formulate the rule described at its beginning: one who redeems his own ma'aser sheni adds a fifth, and in two ways:
"Bein shehu shelo" - that he grew the produce himself.
"U'vein sheniten lo b'matanah" - that it came into his hands as a gift.
The commentators explain that the gift referred to here means that the produce was given to him while it was still tevel, before the ma'aser sheni was separated. For the halachah is that it is impossible to give ma'aser sheni as a gift, since it is "mamon gavo'ah" - it belongs to Hashem and to Heaven, and a person has no ability to give it away as a gift. But if he received tevel as a gift and afterward ma'aser sheni was separated from it, then even though he did not grow the ma'aser sheni himself, since he is the present owner and the principal is his, he must add a fifth.
In summary: in this mishnah we learned the laws of priority in redeeming ma'aser sheni. When both offer a sela, the owner has priority, because he adds a fifth and the ma'aser gains from that. But when the other person adds an issar to the principal, he has priority, even though his addition is less than the fifth, because an addition to the principal is preferable, and because the owner can extricate himself from the obligation of the fifth. We also learned that the obligation of the fifth applies to one who redeems his own ma'aser sheni, whether he grew it himself or received the produce as a gift while it was still tevel.
In the next mishnah we will see how the owner can extricate himself from the obligation to add the fifth.