Commentary for Terumot 4:12

שתי קופות – in each one is fifty Seah [of unconsecrated produce].

Two baskets or two piles and a seah of terumah fell on top of one of them and it is not known into which it had fallen, they bring up the terumah in the other. Rabbi Shimon says: even if they are in two cities, they bring up the terumah in the other. A seah of terumah falls into a basket or a pile of non-sacred produce and it is unknown which of two piles or baskets it falls into. The fact that the terumah could have fallen into either of the two baskets or piles means that the total amount of hullin in the two piles or baskets counts towards the 100-1 ratio needed to take the terumah out of the mixture. Even though the piles and baskets are separate, since we don’t know which the terumah fell into, both count towards the ratio. Rabbi Shimon said that this remains true even if the two baskets or piles are in different cities. For instance a person had a bottle of terumah wine, and he put it into his wine rack and he doesn’t know if he put it in his wine rack in his home in Paris or in his summer home in Nice (a posh mishnah). If there are a total of 100 bottles of non-terumah wine in his wine racks in Paris and Nice, he can give one bottle to the priest (not hard to find in Paris, but perhaps a bit more difficult in Nice) and the rest remains hullin.

ואין ידוע לאיזו מהן נפלה – and both are forbidden from doubt, they assist each other tonullify, and if he wanted to neutralize a Seah from this one, he neutralizes, from that one, he neutralizes, half from this and half from that one, he neutralizes. And these two bins, even if they are in two homes, and it is not known from into which the Seah of heave-offering fell, they neutralize each other, because it is their manner to be vacated, and they are carried from place to place and sometimes are mixed with each other. But two storehouses are not carried; when they are in the same house, they neutralize each other, and if they are in two [houses], they don’t neutralize each other.

ר"ש אומר אפילו הן שבתי עיירות – but the Halakha is not according to Rabbi Shimon.