Aharon Goldfarb asks:
In Tosfos DH Istanis when they say that sicha keshtiya it seems that they are talking on the deoraysa level, whereas the gemara says that the only way you can be meykel is if the issur rechitza is derabanan, that aninus layla derabanan.
Aharon Goldfarb
The Kollel replies:
Tosfos is of the opinion that Sicha on Yom Kippur is only Asur mid'Rabanan, like Tosfos Yeshanim beginning of Perek Yom ha'Kippurim (and Sicha is not like Shetiyah mid'Oraisa, as the Mishnah in Shabbos says "Af Al Pi she'Ein Ra'aya l'Davar..." Shabbos 86A).
Yours,
Mordecai