Why was Yeshaya at the door? (Eruvin 26a)

The gemara concludes that you should not daven at someone's door for them b/c it could entice the Satan (malach hamaves) to come even though Yeshaya davened at Chizkiya's backdoor. The Maharsha asks two obvious questions on this gemara.
1. If you shouldn't do it why was it good enough for Yeshaya?
2. Why was he at the backdoor?

I thought that one question could answer the other. You shouldn't do it at the front door but the backdoor is OK. Not a great answer but it would have been enough for me.

Thankfully though the Maharsha had a much better answer. We can't daven at someone's door because maybe the satan wasn't planning on coming and we will change his mind. Yeshaya, on the other hand, KNEW that the satan was planning on killing Chizkiya so it was OK for him. He was at the backdoor because he also knew that was how the Satan was planning on entering. Helps to be a navi.

Exactly equal (Eruvin 16b)

The Pnei Yehoshua on daf 15a in Sukka gives an excellent explanation to our gemara (15b-16b in Eruvin) which answers a bunch of questions. First a list of some of the questions:

Our gemara paskens like Rav Pappa that if parutz k'omed it's ok as long there isn't more open space than closed space. Tosafos d"h v'hilchasa asks why we pasken here that half and half is ok but in chulin 29a we pasked that half and half is not considered like rov. He "answers" that you could differentiate between mechitzos vs. isur and tumah.

How could the gemara bring a reaya to either Rav Pappa or Rav Huna Brei D'rav Yehoshua from sukka? They each said that the basis of their opinions is the wording of the halacha l'moshe misinai. The halacha was said regarding mechitzos not regarding schach of a sukka.

How can our gemara pasken like Rav Pappa despite the tyuvta?

Is the machlokes really based on a halacha l'Moshe Misinai? Are they really arguing historically what exactly Hashem told Moshe?

He says this also answers some of Tosafos' question in the gemara over there in sukka.

The Pnei Yehoshua says that their machlokes is really based on a much broader machlokes which is actually a machlokes Rishonim. They say that if it's 50-50 then it's treated like a safek. Rav Pappa believes that a safeik d'oraysa is l'chumra but that's only m'drabonnon. Therefore, in this case where it's a d'rabonnon and it's a tircha the Rabonnon allowed you to be meikil and say 50-50 is enough. R Huna Brei D'Rav Yehoshua holds that it's d'oraysa so we will be machmir even in this d'rabonnon by hilchos Shabbos where we will be machmir because of k'eyn d'oraysa tikkun. The gemara asked a question from Sukka because it's a d'oraysa yet we pasken that 50-50 is enough. The truth is that it would have been a question on Rav Pappa also but it was a more obvious question on RHB"Y. Rav Pappa would agree in other cases where it's an isur d'oraysa that we would be machmir. The tyuvta on Rav Pappa was from a case that might have been a reshus harabim d'oraysa in which case even Rav Pappa would agree.

3.14159265 or just 3? (Eruvin 14a)

Someone pointed me to the Tosafos Harosh who asks the obvious question on today's daf. Why does the gemara need a pasuk to prove how to measure the circumference of a circle? Can't we just measure it? He answers that the pasuk tells us that we are allowed to estimate it. The gemara is questioning how does a circumference of 3 mean that the diameter is 1? We know that the circumference would have to be more than 3 to have a diameter of 1!?! The gemara answers that we see from Shlomo that for halachic purposes we can estimate pi to be 3 even though we all know that in reality it's more than 3.

Kilayim requires less than Shabbos (Eruvin 11b)

R' Yochanan and Reish Lakish argue about some kind of a tzuras hapesach that might work for Shabbos and and might work for kilayim. The gemara isn't sure exactly in which case they argue (if it's on the side or top and if it's less than or more than 10) but one thing that is clear is that Shabbos requires at least as much as kilayim to make a wall and maybe more. It could be that this tzuras hapesach will work for kilayim but not Shabbos. Why?

Doors on reshus harabim (Eruvin 6b)

Someone introduced me to Rabbi Yosef Gavriel Bechhofer's blog on halacha of the daf. I found today's post interesting because I was a little confused myself on the concept of doors after learning today's daf. I'll just quote some of it here:

Halacha distinguishes between the enclosure necessary to convert a carmelis into a reshus ha'yachidaand the enclosure necessary to convert a reshus ha'rabbim into a reshus ha'yachid. The Gemara relates that Yerushalayim would have been considered a reshus ha'rabbim had its doors not been closed at night.The Poskim disagree over whether these doors had to have been closed me'd'oraysa or me'd'rabbanan. Some sources maintain that me'd'oraysa a tzuras ha'pesach would have sufficed.Others maintain that in reshus ha'rabbim delasos are required me'd'oraysa. This requirement is limited, in any event, to reshus ha'rabbim. An enclosure intended to surround an area that fall into the category of carmelis does not require doors to allow carrying therein. The rectification of tzuras ha'pesach is sufficient in such cases.

He has some footnotes and more there.

Heker L'mata (Eruvin 5a)

The gemara in the second to last explanation of the machlokes between Abaye and Rav Yosef says that maybe they argue if the heker shel mata is like the heker shel maala or not. Since when is there a heker shel mata?? Until now we've been talking about putting something on the bottom to close up the hole so it would be less than 20 amos. It has absolutely nothing to do with a heker!?! Someone suggested that the gemara is just calling it a heker on the bottom for parallel language even though the purpose isn't to be a heker. That would be possible but I still don't understand the machlokes here. Why should the width of the raised ground be dependent on the size of the heker on top? I can understand if you say the machlokes is based on if you could stand under that or if the reason for the heker on top is really because of mechitza but those were the other answers. What's the svara of the machlokes here?

I don't know an answer to that question but I saw that the Rif understands this gemara differently. He says we pasken that when you put a lower beam because the beam was higher than 20 amos - that beam only has to be one tefach because hekero shel mata is like hekero shel maala. So the gemara isn't talking about raising the ground but is instead talking about lowering the beam (or adding a second beam). The Rosh and the Baal Hamaor don't like this pshat for a number of reasons and I have trouble understanding this pshat also but I think that maybe the Rif felt he was forced into explaining this line differently based on what we said before. If we're only talking about raising the ground then that's not hekera shel mata. The fact that it's called a heker must be because we're talking about something on top.

Eruvin d'rabonnon? - Eruvin 2a

Rav Nissim Gaon asks on the side of the daf how could our gemara say that Eruvin is only d'rabonnon when the gemara on daf 21b and in Shabbos daf 14b says that Shlomo Hamelech instituted it. Doesn't that make it something more than a d'rabonnon? He answers that if it's not written in Tanach then it's still called a d'rabonnon. I find that interesting. We know that if it's written in Nach then that's not a d'rabonnon. Also, if it's something from Moshe then it's not a d'rabonon either even though it's not written in the Torah. I think that it's generally accepted that Eruvin is d'rabonnon by all the Rishonim but I don't know if anyone else has different explanations to explain the apparent stira. I was thinking though that our gemara isn't necessarily a proof. Maybe it all means is that the psul of 20 amos is from the Torah whereas by sukka it's based on the pasuk of "l'maan yaidu.." At first I thought that's what Rashi was saying but then I saw that he said that the entire din eruvin is only d'rabonnon. I think it's pretty clear that eruvin are definitely d'rabonnon but all I'm saying is that our gemara is not necessarily a clear proof.

Siyum Hamesechta (Shabbos 157)

It is customary to find a link between the end of the mesechta and the beginning. The sefer Shabbos Shel Mi says that we learn here that there is a leniency in the prohibition of measuring on Shabbos. For a Mitzvah, it is permitted. The beginning of the mesechta tells us, however, that carrying from one Reshus to another is not permitted even for a Mitzvah, such as giving a donation to a poor person.

Best wishes to all for a g'mar chasima tova!