ab asked:

what is tosfos saying in debu hamatchel kigon?

ab, kew gardens hills,u.s.a

The Kollel replies:

The Gemara teaches that a Loveh (borrower) can force his Malveh (lender) to go to the court of the Loveh's choice only if the court he chooses is very near to the one the Malveh chooses. The example that is given is that of the courts of Rav Huna and Rav Chisda, which were in close proximity.

Rashi explains that they were in "the same place." Tosfos DH Kegon protests that they could not have been in the same place (and at the same time in history), because Rav Chisda considered Rav Huna to be his mentor, and therefore Rav Chisda never passed a Halachic ruling when Rav Huna was nearby. How can he have had a court presiding right next to his mentor's court?

Tosfos answers that the two courts were not in the "same place," but in *relative* proximity; three Parsa'os from each other. At that distance, Rav Chisda felt comfortable passing Halachic rulings (since one is permitted to pass rulings when he is more than 3 Parsa'os from his mentor). Nevertheless, since they were relatively nearby to each other, the Loveh may force the Malveh to go to the one instead of the other.

M. Kornfeld