- If חומש is calculated מלגיו or מלבר
On the previous Daf, the Gemara asks: חומשא מלגיו – is the additional fifth (paid for redeeming maaser sheni and other cases) calculated from inside (i.e., a fifth of the redeemed principal), או חומשא מלבר – or is the fifth calculated from the outside (i.e., a fifth of the final total, which is a fourth of the principal)? Ravina quotes a Mishnah discussing redeeming an ancestral field which one was makdish, which is given to the highest bidder. It teaches that five is added to a bid of twenty, proving that חומש is calculated “from the outside.” This is a machlokes Tannaim in a Baraisa, about the passuk "ויסף חמישיתו עליו" – and he shall add its fifth onto it (i.e., the hekdesh non-kosher animal being redeemed). Rebbe Yoshiyah says: שיהא הוא וחומשו חמשה – it mean that it and its fifth shall together be five (i.e., the fifth is calculated from the “outside”). Rebbe Yonasan says: חמישיתו חומשו של קרן – its fifth means a fifth of the principal (i.e., from the “inside”).
- חומש מעכב או אינו מעכב
The Gemara asks: חומש מעכב או אינו מעכב – is adding a fifth essential to redemption, and redemption is ineffective until it is paid, or is it not essential to the redemption? Do we say four zuz of maaser sheni are redeemed with four zuz, ואכנפשיה מוסיף חומש – and he adds a fifth on his own, or do we say that four zuz are redeemed with five? Ravina quotes a Mishnah teaching that redeeming דמאי does not require a fifth, and explains that the principal, which is essential for redeeming Biblical maaser, is required for דמאי, as opposed to the חומש, which is not essential for Biblical maaser. The Gemara suggests this is a machlokes in a Baraisa, which teaches that if one gave the principal but not the חומש, Rebbe Eliezer says he may eat the maaser, Rebbe Yehoshua says he may not, and Rebbe says he may eat it only on Shabbos (as a leniency for Shabbos’s honor). However, Rav Pappa concludes they all agree the חומש is not essential but disagree if he was prohibited from eating the maaser out of concern he may be negligent in giving the fifth. A similar machlokes appears regarding hekdesh, and Rebbe Yochanan says that all are lenient on Shabbos regarding hekdesh, because the treasurers will demand the fifth from him.
- Paying a חומש on a חומש
The Gemara discusses a חומש payment engendering another חומש payment. Rava quotes a Mishnah which teaches, based on a derashah, regarding one who stole and swore falsely to deny it, who repays the principal plus a penalty of a fifth, that if he paid the principal and then swore falsely to deny owing the fifth, הרי זה מוסיף חומש על חומש - he must add an additional fifth to that original payment of a fifth. Another Mishnah teaches about a non-Kohen who eats terumah unintentionally, who must replace it with chullin produce plus a fifth, that if he later eats that fifth, he repays it plus a fifth of that fifth. Regarding maaser, there are no sources discussing it, and Rava says there is no question about it, and Rashi explains that redeeming its fifth definitely does not obligate another fifth. Rava asks regarding hekdesh, if one pays an additional fifth when redeeming a fifth payment. After explaining the question, the Gemara quotes Abaye teaching that the Torah juxtaposes חומש with כסף ערכו – the money of its evaluation (the principal), teaching that just as the principal obligates a חומש, the חומש does as well.