Who says?-Who remembers? Unbelievable Gaonos From Reb Pinchas Hirshprung

דף השבוע ברכות ל"א ע"א אל יפטר אדם מחבירו אלא מתוך דבר הלכה שמתוך כך זכרהו Reb Pinchas Hirshprung Dr. T. Juda Shlita told me that he once asked his father in law (R. P. Hirschprung  zt"l) the following question: The Gemoro says If one wants to take leave from his friend, he should do so by saying a Dvar Halacha, by doing so, he will remember him. Dr. Juda asked, who is the one that is supposed to say the Dvar Halacha and who is the one who remembers?. Is it the one that stays behind or the one who leaves? R. Hirschprung answered, that probably the one who is leaving says the Dvar Halacha and the one who stays behind, remembers. Dr. Juda asked him why not the other way round, the opposite? R. Hirschprung responded:  "yes it could be the opposite". (The one who stays on says the Dvar Halacha etc.) Dr. Juda asked again, perhaps both have to say the Dvar Halacha & both of them remember each other? R. Pinchas Hirschprung again, responded,  "yes, it could be".   Dr. Judah said  " The Shver surely knows of a Chazal which of three is the correct way." Rabbi Hirschprung closed his eyes and starts scanning through Shas in his head. Within a minute or so R. Hirschprung blurts out "Eruvin 64a at the bottom of the עמוד." CLICK HERE TO SEE ERUVIN 64a