Rav Yitzchak says that anyone who says rachav rachav will emit seed and then rav navhamn says I did it and nothing happened.
Well isn't it a problem to waste seed so therefore why did he experiment because then it would be zera levatala and aren't we supposed to run away from lust , but it says that anoyone who says rachav name will be taken with lust ?
Mordechai yusupov, Queens, usa
You should ask an even stronger question: Rebbi Yitzchak himself just said those words when discussing the Halachah, so Rav Nachman should have asked him about that! However, the Machaneh Chayim suggests that there are three different ways to say "Rachav, Rachav":
1) When one has no thoughts about women;
2) When one wants a beautiful woman for his wife;
3) When one lusts after a beautiful woman in front of him.
Chazal say (Sotah 8a) that the Yetzer can have control only on what a person sees, and in this case there is no woman there, so Rav Nachman thought it was alright to say. However, he thought Rebbi Yitzchak was saying that if a person even thinks of a woman without seeing her he will have a mishap, and Rebbi Yitzchak answered that this is only if he actually saw her once, as then the Yetzer ha'Ra can have control on him.
It is also possible that Rav Nachman was saying that he had said it in the past and nothing happened to him, or that he was pointing out to Rebbi Yitzchak that he (Rebbi Yitzchak) himself had said it and therefore it was not a problem. (Interestingly, in one tet of the Gemara in Megilah, it says that Rav Nachman said, "I said Rachav, Rachav," and in another text it says that Rav Nachman said, "I said it." However, I saw in a number of manuscripts of Megilah that Rav Nachman says, "I said it," without mentioning the name.)
Yoel Domb