Siman - Eruvin Daf 15

• לחי העומד מאליו

There is a machlokes Amoraim regarding, לחי העומד מאליו – a lechi that happens to be positioned properly at the side of the mavoi but was not originally placed there to adjust the mavoi, such as a tree. Abaye said it is valid and Rava says it is not.

The Gemara clarifies that everybody agrees that it is not a valid lechi when they did not intend to use it as a lechi erev Shabbos, as they were planning on using another lechi that subsequently fell. The machlokes is in the case where they intended erev Shabbos to use it as a lechi.

After determining through a number of proofs that Abaye and Rava agree that a mechitzah that  

was not originally erected as a mechitzah is valid, the Gemara concludes that Abaye says the lechi is valid because he holds a lechi serves as a mechitzah, and Rava says it is invalid because he holds a lechi serves as a heker, and it will only serve as a reminder if it was originally erected as a lechi.

• Writing a Get on an animal

The next Mishnah introduces a number of machlokism regarding using living things for lechis, tomb covers and gitten. Regarding gitten, the Tanna Kamma holds, כותבין עליו גיטי נשים – one may write a get on living things, ורבי יוסי הגלילי פוסל – and Rebbe Yose HaGlili invalidates such a get.

The Gemara explains that both the Tanna Kamma and Rebbe Yose HaGlili derive the halacha from the same passuk, וכתב לה ספר כריתות – and he shall write for her a bill of divorce.

•Rebbe Yose HaGlili learns from וכתב לה, that one may write it on any type of writing surface, not just parchment, whereas ספר teaches that it must be written on something similar to a ספר, not food or living things.

•The Rabbanon learn that וכתב לה means that she cannot be divorced with money, and ספר teaches, לספירות דברים בעלמא הוא דאתא, that it should be a narration of words that convey that he is divorcing her.

• A caravan camped in open fields

The next Mishnah teaches that if a שיירא שחנתה בבקעה - a caravan encamped in an area of open fields, which is considered a karmelis, that surrounded itself with animal trappings such as saddles and saddle bags to serve as partitions, may carry within it, provided that:

1. שיהא גדר גבוה עשרה טפחים - The partition must be ten tefachim high.

2. לא יהא פירצות יתירות על הבנין – The total gaps should not be more than the total walls.

3. כל פירצה שהיא כעשר אמות מותרות מפני שהיא כפתח – An opening of ten amos is considered a doorway and they can carry there. More than ten amos is considered a breach and carrying would be forbidden.