Demai, Chapter Five, Mishnah Four
In the previous mishnah we learned of how one tithes when one buys loaves of bread from an am haaretz baker. Here we learn how one tithes when one buys from a bread seller, the merchant who buys bread from the bakers to sell it retail.
1) If one bought from a bread seller he must tithe every mould [separately], the words of Rabbi Meir.
2) Rabbi Judah says: he may give tithes from one mould for all the others.
3) But Rabbi Judah agrees that one who bought from a monopolist he must tithe every mould [separately].
Section one: Rabbi Meir is strict and rules that one must separate tithes separately for each type of mould. Each baker would use a slightly different mould to shape his loaves, and therefore loaves of different moulds can be assumed to come from different bakers.
Section two: Rabbi Judah holds that bread dealers buy from only one baker. Therefore, even if there are different moulds, he can separate tithes from one for the other.
Section three: Rabbi Judah agrees that if one bread dealer has a monopoly over selling bread in the city, then he must tithe for each mould separately. In this case, since he is the only one selling bread in town and there is more than one baker, it is obvious that the bread seller has bought from more than one baker.
Interestingly, the Hebrew word for monopolist is monpol. This is the first time Ive ever seen that word in rabbinic Hebrew. Cool.