English of Core Text: Rav Yehudah said in the name of Rav: All rivers are lower than three rivers, and the three rivers are lower than the Euphrates. But it is written “and the fourth river is the Euphrates”? Rav Nachman bar Yitzchak said: It is the Euphrates of the original [source].
On the daf / in context: The hierarchy of rivers is established; the Euphrates is the primary source from which the others ultimately derive.
Type of Learning: Custom (hierarchy of rivers / primacy of Euphrates)What Is Learned: The Euphrates is the highest/source river; the others are subordinate to it.