I spoke this week about an interesting kasha on the Rambam, The Rambam paskens that gid hanasheh is muttar b'hana'ah and one can give it or sell it to a non-Jew. The problem is that there is a sugyah in Pesachim 21b-22a that has a machlokes between Chizkiyah and Rav Avahu. Chizkiyah holds that whenever the Torah says Lo Tochal it means the food is assur to eat but it doesn't tell you whether the food is assur b'hana'ah. Rav Avahu holds that whenever the Torah says Lo Tochal it means the food is assur and is also assur b'hana'ah. The gemra asks on Rav Avahu that we find by gid hanasheh that it says "Lo Yochal", yet it is mutar b'hana'ah. The gemara answers that gid hanasheh is included in neveilah and just like neveilah is muttar b'hana'ah so too is gid hanasheh. The gemara answers that only works if you hold gid hanasheh has ta'am-taste. But if you hold "ein b'gidin b'nosein ta'am" and eating it is like eating a piece of wood, then you can't include gid hanahseh in neveilah. The gemara answers ain hachi nami, if you hold "ein b'gidin b'nosein ta'am" then gid hanasheh is assur b'hana'ah and this is shittas R' Shimon.
The problem with the Rambam is that he paskens "ein b'gidin b'nosein ta'am" and also paskens that gid hanasheh is muttar b'hana'ah. According to the gemara, these two halachos can't co-exist. A number of Achronim attempt to answer the Rambam. One mehalech is found in the Kovetz Shiurim Pesachim Siman 90. The Rambam only counts cooking meat and milk and eating meat and milk as separate lavin. He doesn't count the issur hana'ah of meat and milk as a lav (even though it says "lo sevasheil gidi 3 times). The Rambam writes in Lo Saseh 187 the reason is becasue the issur achilah is really just a form of hana'ah. When the Torah says "Don't eat" what it is really saying is don't have hana'ah-whether by eating ir bu some other form. This is pshat in Rav Avahu who says that whenever the Torah says Lo Tochal it means the food is assur and is also assur b'hana'ah. The torah uses the loshon of eating cause this is the main form of hana'ah.
Rav Elchanan says that this idea of the Rambam can only apply to a case where you get hana'ah by eating the food. However, by gid hanasheh the Rambam holds "ein b'gidin b'nosein ta'am" -there is no hana'ah by eating a gid hanasheh. Al karchach you have to say that the issur achilah of gid hanasheh is the ma'aseh achilah and has nothing to do with the hana'ah. Mimeila the whole drasha of Rav Avahu doesn't apply to gid hanasheh and it is actually muttar b'hana'ah.
Rav Elchanan says this is pshat in the Ramban who answers the kasha on the Rambam by saying that when the gemara said it's R' Shimon it was only l'ravcha d'milsa. Meaning really the gemara could have given this teretz but it said we are going with shittas R' Shimon l'ravcha d'milsa.
(ayin Rabbi Akiva Eiger in Pesachim who rejects this approach.)