(Mishnah): If a person had two baskets of Tevel in front of him and he said, "Let the Maaseros of this be on that and of that be on this" - (only) the first is thereby tithed.

If he said, "The Maaseros of these - each basket's Maaseros are in the other", he has thereby (successfully) declared (their tithes).

(Gemara) (Tosefta): (About the Mishnah's first case - how does he fix up the second basket? If each basket contained 100 figs,) he takes two and two tenths and two hundredths (2.22) figs. (Usually when taking Maaser Rishon, for every 10 figs, one becomes Maaser Rishon - so one fig fixes up 9 figs. Here, he is taking Maaser Rishon from basket two for basket one, as well as for itself, so to fix up all 100 figs of basket one, he must take 11.1 figs from basket two. Terumas Maaser (which is the only part that must actually be removed) is 1/10th of the Maaser Rishon, meaning 1.11 figs. But since he is also fixing up the 100 figs of basket two, the total Terumas Maaser is 2.22 figs.) (Note: This explanation follows the Vilna Gaon.)

(Shmuel): The Baraisa cannot be taught this way! If he separates one part for ten (he has only fixed up 9 of those 10 parts), so he must still separate a further one part for 100 (i.e. 1/100th) for the Maaser Rishon of that part that wasn't fixed up. If he separates that further one part for 100, he still only fixes up 9/10th of what must be fixed up and he must still separate a further 1/1000th for the Maaser Rishon of that part that wasn't fixed up. And if he separates that further 1/1000th, he still only fixes up 9/10th of what must be fixed up, and he must still separate a further 1/10000th for the Maaser Rishon of that part that wasn't fixed up.

(R. Yosi bar Chaninah): For what he did to basket one, he has negated a positive mitzvah (of taking tithes in the correct order). For basket two, he both negates a positive mitzvah and transgresses the negative mitzvah (of tithing in order)...

For basket one, he negates a positive mitzvah - because he designated two tithes at the same time.

For basket two, he both negates a positive mitzvah and transgresses the negative mitzvah - because he designated two tithes at the same time and because he separated Maaser Sheni of the basket one before Maaser Rishon of basket two.

(R. Eliezer): (The Mishnah taught that if the declarations were made one after the other, only the first basket is tithed but not the second.) This is the opinion of R. Meir, who said that if someone said two contradictory statements, you only consider the first one.