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1. The Mishnah discusses using a bolt (to lock a door) that is tied to the door by a long string and therefore drags on the ground.
2. Shmuel rules according to the opinion of Rebbi Yehudah.
3. Rebbi Tavla allowed the bolt to be tied to the doorpost in order to use it on Shabbos.
4. We find that the Amora'im permitted using various items to help lock a door as long as they are considered vessels.
5. One is allowed to add onto a structure which is considered a temporary tent on Shabbos.
A BIT MORE
1. The Tana Kama: One may not use the bolt to lock the door, except inside the Beis ha'Mikdash where Rabbinic prohibitions of Shabbos are suspended. Rebbi Yehudah: One may use it to lock the door anywhere, provided that it is tied to the door. In the Beis ha'Mikdash, one may use it to lock the door even when it is not tied to the door.
2. Rava says that this ruling applies only when the item is tied to the door itself, not just to the doorpost.
3. However, this was only if the bolt was tied with a strong rope.
4. Rebbi Pedas permitted using a huge beam to prevent people from coming in the door, since it had been used as a bench.
5. For example, if a blanket was rolled up into a width of a Tefach before Shabbos, one may roll it out and extend it to serve as a roof on Shabbos, since it was already a roof before Shabbos. However, if it did not form a covering of at least the size of a Tefach before Shabbos, one may not extend it on Shabbos.
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