Avoda Zara 44a - Space for 2 Tefillin

The gemara says that there was enough room on the head of Dovid Hamelech to wear both the crown and tefillin because there is enough space on the head for two tefillin. Rashi strangely focuses on there being enough space for two straps to encircle the head, rather than focusing on the actual boxes of the tefillin It seems that rashi does this due to the context of the sugya that requires space on the head for the entire crown to encircle the head and have the tefillin, so there must be space for two tefillin to entirely circle the head. However, Tosafos in Eruvin 95a explains that it would certainly be true of the boxes because the kohen gadol wore the tzitz not on his forehead but on the place of tefillin, yet there was also space for tefillin between the tzitz and the hat - clearly there is space for two pair of tefillin one behind the other.

From Tosafos it seems that the space for two tefillin would only be one behind the other but not one adjacent to the other. This would conform with the assumption that the tefillin must be perfectly centered, which would obviously not be possible if one wore two tefillin adjacent to one another. However, the Beis Yosef interpreting the Rambam seems to understand that there is space for two pair of tefillin even one next to the other. This seems to be the assumption of the divrei chaim (sanz) - see here - who holds that the tefillin need not be perfectly centered (which would explain many gedolim pictures!). The editor of the divrei chaim strangely attributes his comment that insistence on the tefillin being perfectly centered is דברי בורות - words of a bor, to be the nesivos who says that it shouldn't be moved to this side or that. But, in actuality the source of this ruling is the Shulchan Aruch Ha'rav (Gra"z) 27:18 - צריך לכוין הקציצה שתהא באמצע רוחב .הראש כדי שתהא כנגד בין העינים It is the ruling of the Ba'al Hatanya that the divrei chaim refers to as "divrei boros".

Avoda Zara 39b - Will Goyim Switch Even For No Benefit?

I posted previously that Tosafos holds that a goy is not chashud to cheat without any benefit, even if it won't be detrimental to him either. http://hearos.blogspot.com/2010/09/avoda-zara-31b-relying-on-kashrus-seals.html

It is difficult to figure out Rashi's opinion on this issue. The gemara 34b that says goyim aren't suspected of adding wine to murayus because קסתא דמורייס בלומא קיסתא דחמרא בד' לומי implies that only when it cost more to add wine will they be deterred from doing so, but for no gain they may cheat. Rashi seems to assume like this because when the gemara says that the first and second making of the murayos "doesn't need" wine to enhance the flavor, rashi writes - איידי דנפיש שומניה פעם ראשון ושני מקלקל להו חמרא. Why would Rashi have to say that the wine would "ruin it"? Rashi seems to hold that even if the goy has no reason to add wine, he may do it anyway.

Rashi in our sugya also seems to follow this approach. The gemara says that there is no reason for a goy to swap the kosher bread for the non-kosher bread. Rashi writes that since he has no benefit in swapping it, one seal is sufficient - כיון דאיכא חותם אחד, לא טרח ומזייף במידי דלית ליה רווחא. Since he has nothing to gain, why would we require any seal at all? This question is raised by many achronim (mateh yehonasan [r. yonasan eibcschitz] in y.d. 118:10, gilyon maharsha, darchei teshuva). The achronim suggest that although he has no monetary gain in swapping the breads, he may be motivated to do so because he is hungry now and later replaces it with treif bread so one seal is enough to avoid the practical motivation. However, rashi may go li'shitaso that to permit it without a seal, it is not sufficient that the goy has no benefit, rather we require that the goy would actually suffer a loss. The Ritva quotes the ramban that Shmuel in our sugya argues on Rav and permits the bread without any seal at all - this would be consistent with Tosafos 12a that whenever there is no motivation to swap we don't have to be concerned.

See Rashi 64b d.h. aval, where he seems to hold that if the ger toshav has no benefit, we don't have to be concerned for a swap. This would contradict the above approach, but perhaps we are more lenient for a ger toshav than for a goy.

Avoda Zara 38a - Answering the Contradiction in Rashi

Yesterday, I pointed out that rashi contradicts himself in describing why chazal made a gezeira against bishul akum. Rashi on the mishna says it is one of the decrees meant to prevent intermarriage, whereas rashi on the gemara says that it is a kashrus concern to avoid eating something not kosher.

The gemara 36a had a machlokes why and when chazal made a gezeira on oil (that r. yehuda ne'siah, the grandson of rebbi later removed). Rav says that it was made by Daniel to prevent mingling and intermarriage with goyim, but Shmuel says that it is a kashrus concern since they cook the oil in their non-kosher pots. Tosafos writes that even according to Shmuel the primary gezeira is an intermarriage concern, just that chazal realized that permitting oil will not lead to intermarriage like drinking wine with goyim will (as rashi explains 36b - wine "burns" in a person, meaning that it instigates the yetzer hora). Therefore, chazal needed to support the gezeira on oil by articulating an additional concern of the treif pots. This concept can be further explained based on an idea that R. Moshe writes (igros moshe y.d. 1:43:2) - Chazal don't like to create gezeiros out of thin air. They only make a gezeira if there is some remnant or clear connection to an issur d'roaysa. They need the issur d'oraysa to create the framework for the gezeira, even if the actual concern is something else. Similarly, they didn't want to create a gezeira on oil without a clear association to an issur d'oraysa because the connection between intermarriage and oil is very loose. That is why they had to create a framework of the treif pots in order to forbid oil.

Perhaps rashi is telling us the same thing regarding bishul akum. The motivation to assur it is intermarriage as rashi writes in the mishna, and is clear from the association to oil and bread. But, since it is not clear how eating beans of goyim will lead to intermarriage, the framework of the gezeira had to be as a concern that the goy will feed the jew something that isn't kosher. Tosafos merely rejects the kashrus concern as the primary motivation, but understands that it can be used to create the framework and therefore explains that even when something is cooked in the home of a Jew it will be assur. Although the intermarriage concern doesn't apply, it would be assur since the framework is to assur anytime a goy cooks something from start to finish because they may not be careful about the kashrus of the ingredients.

Avoda Zara 37b - 38a - Bishul Akum

The gemara begins its discussion about the parameters of bishul akum. However, more fundamentally is understanding the rationale for the gezeira on bishul and pas. Tosafos explains that from the fact that the gemara uses the term מנהני מילי to introduce the discussion about bread and even cites a pasuk, implies that it is d'oraysa, until it concludes that it is only d'rabonon. For the gemara to make such a mistake and think that it was d'oraysa implies that it is a very early gezeira, that predates the gezeira on bread made by shamai and hillel. This is how Tosafos explains why the gezeira on pas failed to be accepted, whereas the gezeira on bishul was and remains strong - they are two separate gezeiros on two separate entities, so the leniency on bread doesn't affect "shlakos" (cooked foods).

There is a very difficult contradiction in rashi that is even pointed out by Tosafos. Rashi in the mishna says that the gezeira on shl'akos is because of intermarriage, but on the gemara 38a rashi says that it is to prevent the jew from eating in the non-jews home since it will lead him to eventually eat not kosher. According to Rashi's explanation in the gemara that the gezeira on shlakos is more of a kashrus concern, it certainly would have nothing to do with the gezeira on bread. However, the contradiction in rashi is very difficult?

Tosafos is also hard to understand. Tosafos quotes Rabbeinu Avrohom who says that the issur of shlakos only applies to food cooked in the home of the goy, not to food cooked in the home of the Jew. Tosafos disagrees because - לא חלקו כלל חכמים בין רשות הישראל לרשות העובד כוכבים כי לעולם יש לחוש .שמא לא יזהר גם בביתו של ישראל כמו בביתו של עובד כוכבים Tosafos had already rejected rashi's approach that the issur is a concern of kashrus that the goy will feed the Jew something not kosher, yet Tosafos rejects Rabbeinu Avrohom by saying that even in the house of the Jew the concern of feeding the Jew something non-kosher applies?

Avoda Zara 33b - Miluy V'iryu vs. Hag'ola

The gemara on amud alef discusses the process of miluy v'iruy confirming that it would work to kasher from yayin nesech even for earthenware. Yet, the gemara on amud beis says that "kinsa" which would be a light burning on the inside of the vessel would not be sufficient to kasher for yayin nesech. Rashi (d.h. v'hilchisa) makes a logical assumption that something heated by fire cannot be better than fire itself, therefore if "kinsa" doesn't work, neither would hag'ola with hot water. The obvious conclusion is that miluy v'iruy would prove to be a better form of kashering (at least for items that absorbed without heat) than hag'ola. The chidushei anshei sheim (printed on the pages of rif) confirms that this is indeed the opinion of rashi, which is against the seifer ha'terumos who says that whenever miluy v'iruy works, hag'ola would certainly work. Tosafos in the name of Rabbeinu Tam also seems to assume that even a minimal hag'ola that would not normally work for issurim (such as pouring in hot water and swooshing it around the barrel) would work here. This would be consistent with the sefer ha'terumos that even a minimal hag'ola is better than miluy v'iryu, so a proper hag'ola would certainly work whenever we allow miluy vi'ruy - unlike rashi.

I would like to offer another interpretation of rashi, so that rashi would be consistent with the sefer haterumos and Rabbeinu Tam. The sefer toras habyais (re'ah) writes that there is a big difference between kashering through hag'ola and kashering through libun. Libun burns the issur in its place whereas hag'ola is "maflit" - extracts the issur. Rashi's kal v'chomer that if "kinsa" doesn't work, certainly hag'ola wouldn't work is true from the perspective of burning out the issur. Since the actual fire cannot destroy the issur, a product of fire i.e. hot water certainly cannot destroy the issur. This is all within the realm of "libun", meaning when hot water is going to use the mechanism of kinsa which rashi holds is the only mechanism possible by earthenware (because hag'ola doesn't work for earthenware as the gemara says in pesachim). Rashi never entertains actual hag'ola extracting issur because it doesn't work by earthenware. However, miluy v'iruy which allows for 72 hours of diluting will be a better form of extraction of issur than hag'ola for earthenware since hag'ola doesn't work remove the issur. But, for other materials such as metal, where hot water can work as hag'ola and not just as a way of destroying the issur, rashi may very well agree with the sefer haterumos and tosafos that whenever miluy v'iruy would work, hag'ola would certainly work.

Avoda Zara 32a - Rotzeh B'kiyumo

The gemara questions whether one is allowed to use a piece of clay that has wine of a goy absorbed in it, since by doing so he is interested in the existence of the issur. The question is predicated on the assumption that it is forbidden to do something with issur hana'ah that indicates you want it to be in tact. The only question that the gemara has is when your interest is not in the issur, rather in the item that is holding the issur i.e. the clay, whether the prohibition applies. Although the gemara seems to be concerned that there is a problem of being רוצה בקיומו על ידי דבר אחר, it isn't clear if this would apply to things other than the special hadrayni clay. The gemara at the very end of the discussion makes a distinction between the 'cheres hadrayni' and 'kankanim'. The gemara says that the wine absorbed in "kankanim" - bottles, is not in tact. Tosafos questions whether this girsa is accurate, or should be deleted from the gemara entirely. Therefore, Tosafos concludes that if the girsa is deleted, we would apply the issur to other cases of a vessel that has issur hana'ah absorbed in it, whereas if the girsa remains we would not apply it to other cases. Two obvious situation would be a vessel that has either chometz or meat and milk absorbed in it, which are both assur to benefit from, would it be permitted to get some use from the actual vessel. Tosafos says that some poskim consider this assur, but Rabbeinu Tam who keeps the girsa in the gemara rules that it is permitted to use a vessel of chometz or bassar v'cholov to store something in.

The Shulchan Aruch (o.c. 450:7) says that one cannot lend a pot to a goy over pesach because the goy will cook chometz in it and the jew will want the actual chometz to be there since otherwise the pot would get too hot and break. This is not a case of רוצה בקיומו על ידי דבר אחר, rather a classic case of רוצה בקיומו of the actual issur. However, the Rama says that one can use a chometz pot to heat water for bathing and other uses, implying that he holds that we permit a situation of רוצה בקיומו על ידי דבר אחר by other vessels containing issur hana'ah. It is only by the hadrayni clay that it is forbidden since it is considered to be in tact, as Rabbeinu Tam paskened.

Avoda Zara 31a - Drinking Beer and Coffee

Prohibition to drink beer in bars:

The gemara asks why beer of goyim is forbidden. However, the question doesn't stem from any statment, rather the question compels the assumption that it is actually forbidden. The gemara says that it is assur either because of leading to intermarriage or because they leave the water uncovered. Yet, the gemara says that the opinions who forbid beer due to intermarriage, permit it when taken out of the bar, store or home of the goy. Bishul Akum is also prohibited dues to intermarriage, yet we don't find any leniency of take out - why? Tosafos points out that we don't find this prohibition in any Tanaic source, so it must have been an issur first introduced by the amoraim. It seems that the amoraim created an issur to prevent intermarriage similar to the earlier prohibition (i.e. bishul akum and pas akum), but weren't quite as strict in their prohibition and permitted it to be taken home [Taz (114:2) offers other reasons why we are more machmir with bread than beer]. Tosafos goes one step further and justifies the practice of drinking beer when travelling and staying over in an inn of a goy by suggesting that it was only assur if done with some form of regularity, or in a place established for drinking such as a bar, but not when done באקראי בעלמא. All this is codified by the shulchan aruch 114:1.

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Bishul Akum on Beer and Coffee:

Another issue that Tosafos raises - why isn't beer forbidden as bishul akum? Tosafos answers: 1. It isn't fit for a kings table. 2. Just like for the bracha we consider it batul to the water and make shehakol, it is also batul for the purpose of bishul akum. The second answer of Tosafos is cited by the Shach (114:1), Taz and even Gr"a (3). The problem is that Tosafos in Brachos 38a asks why we don't make mezonos on beer that is made with barley. Tosafos answers: 1. there is no actual barley in the water, just the taste of barley. 2. since they have a more ideal use i.e. bread, it is only shehakol when not eaten as they are meant to be eaten. 3. drinks are always shehakol. Howe can Tosafos by us say that we make shehakol on beer because it is batul to the water (and uses this as a source that there wouldn't be bishul akum), since Tosafos in Brachos offers 3 other answers as to why we make shehakol? It seems to me that the first answer in brachos is really the same explanation as Tosafos is offering by us. Since there is not actual barley in the water, just the taste of barley, it isn't considered chashuv and is batul to the water. Even though Tosafos in Brachos seems to hold that the last answer is the primary one (it is repeated at the end of the page), it is not meant to reject the first answer since that would undermine the heter of bishul akum.

Now, is coffee a problem of bishul akum? Pischei Teshuva (114:1) cites pri chadash that the same heter we have for bishul akum by beer would apply to coffee. The panim me'iros disagrees because he understands that the primary heter for beer is that it isn't fit for a kings table, which is not the case by coffee. Based on this he holds that coffee cannot be purchased from goyim. The Yad Ephraim explains (in the name of pri chadash) that the heter of not being fit for a kings table is applicable to coffee as well because the rule is actually - כל שאינו עולה על שולחן מלכים ללפת בו את הפת, meaning that even if fit it is served at a kings table, since it doesn't enhance the bread it is not included in the prohibition of bishul akum.

Avoda Zara 31b - Relying on Kashrus Seals

Years ago when items that were sent in the hands of goyim were not professionally sealed, there were very specific signs that were made on the packaging to assure that it was not opened by the goy. But, nowadays where we have large kashrus organizations approving items that are packaged and sealed in many different ways, we are compelled to analyze what type of seal and packaging is sufficient to remove the concern that the contents weren't exchanged.

First, it is important to note that all these rules are only applicable if the goy would have some motivation to switch the kosher item for a non-kosher item, as Tosafos 12a (and 32a) writes. Generally, a goy would have no motivation to swap one item for another since the kosher item isn't better or more valuable to him that the treif one. Secondly, the professional packaging may in and of itself qualify as a double seal since it is almost impossible for an individual to duplicate a factory sealed item. Nevertheless, it is worthwhile to explore the halacha in this area.

In the Braisa 31a there is a machlokes whether items sent in the hands of a goy require a double seal (Rabbonon), or whether it is sufficient to just have one seal (R. Eliezer). The gemara paskens like R. Eliezer that a single seal is enough. But, Tosafos points out that Rav on 39a holds that for certain (expensive) items including meat and wine a double seal is necessary. How does this fit with R. Eliezer who permits a single seal on wine? Tosafos offers two approaches: 1. When sent in the hand of a mumar (which would probably include a jew who doesn't keep kosher) a double seal is required since he is self righteously assumes he will be trusted and is more likely to cheat. But when sent in the hand of a goy, one seal is sufficient (Tosafos rejects this approach). 2. When the seal will be checked in the end, one is sufficient, but if it won't be checked such as when sent from one person to another, it is necessary to have 2 seals.

Tosafos 32b confirms the approach that an item must either have 2 seals or be checked in the end, based on the braisa which says - אם מכיר חותמו וסתמו מותר. Rashi clearly understands that even according to R. Eliezer, it is necessary to check up on the seal and recognize that it wasn't tampered with. In the the retail market place when the sender doesn't check up on the seal, Tosafos holds that it should either require 2 seals, or a letter to the receiver describing the seal plus notifying the goy that the receiver will be checking up on the seal (it is clear from Tosafos that the letter doesn't replace recognizing the seal and only works because the goy is aware of the letter and scared to switch the item). However, Tosafos writes in the name of Rabbeinu Tam that according to R. Eliezer, the rationale to allow a single seal is that we aren't afraid that the goy will swap the item, so it isn't even necessary to check up on the seal. But, Tosafos only relies on this bidieved since the braisa does require recognizing the seal. At the very end of Tosafos they offer an alternate p'shat in the braisa that recognition of the seal is unnecessary. The requirement to recognize is only to the exclusion of one who finds the seal to be tampered with, but without any knowledge either way it is permitted - but concludes והמחמיר תבא עליו ברכה.

The discussion until now is when the item was received with at least one seal. However, the Rama (y.d. 130:8) is even matir when the seal is found to be broken, so long as it seems that it was broken accidentally and not tampered with. However, the Nodeh B'Yehuda (pischei teshuva 2) limits the Rama to a case where the goy isn't aware that the seal was broken, but if he was aware that it was broken, albeit accidentally, the wine or meat remained in his hands without a seal. Based on this, if one would purchase a kosher product (i.e. meat or cheese) in a store and the package was opened, it would still be permissible because we can assume that the goyim who work in the store aren't aware of the broken seal. But, if they would notify you of the broken seal, even if they would say that it opened when it fell, it would be forbidden to use the product.

Avoda Zara 26a - Permitting Issurim for Eivah

Is eivah - animosity - a good rationale to permit the violation of all issurei d'rabonon, or only when the gemara stipulates on a specific issur that it is permitted for eiva, would we allow it? The gemara understands that the issur d'rabonon of assisting a goy in child birth would be permitted for the sake of eivah. However, on shabbos it would not be permitted since the eivah can be avoided with an excuse that we only violate shabbos for those who keep it. The gemara seems to imply that had we not had a good excuse we would even permit the violation of shabbos to avoid eivah - animosity. Tosafos asks that we never find that an issur d'oraysa would be permitted for the sake of preventing animosity? Tosafos answers that we are speaking when the baby is almost out, so the pulling it out wouldn't constitute an issur d'oryasa, and we would only permit actions that would be d'rabonon. There may be an implication in Tosafos that we would permit all issurei d'rabonon to prevent eivah. However, the Ritva says that we can't permit all issurei d'rabonon for the sake of eivah unless chazal stipulated in the original gezeira that it should be mutar to avoid animosity.

However, it seems clear that even Tosafos holds we cannot freely be matir all issurei d'rabonon for the sake of eivah. Tosafos 2a discusses why we are lenient to allow business with goyim within 3 days of their holiday. Initially, Tosafos suggests that to avoid business with them would create animosity, which would allow the violation of an issur d'rabonon. But, Tosafos doesn't say it matter of factly, rather proves from a gemara 7b that this specific issur d'rabonon that prohibits business within 3 days of their holiday is permitted to avoid eivah. Tosafos continues by rejecting the proof - the story of R. Yehuda Nesiah doesn't indicate that it would be permitted to violate to avoid eivah, rather he was looking for a way to avoid both the violation while still avoiding the eivah. Now, if Tosafos would hold that eivah is a blanket heter to allow all issurei d'rabonon, the rejection of the proof shouldn't impact the din that for eivah it is permitted to do work with them. Clearly, Tosafos understands that without a proof from the gemara that this specific issur would be permitted to avoid animosity, we would have to assume that the concern of eivah isn't even strong enough to push off an issur d'rabonon (unless specifically stipulated by the gemara).

Similarly, Tosafos on the bottom of 26b quotes a gemara to prove that one is allowed to heal a goy if there is payment since otherwise it would create eivah. If every d'rabonon is mutar to prevent eivah, why does Tosafos need a proof from a gemara in gittin 70a that there are circumstances in which you can heal a goy? It must be that not every d'rabonon is mutar to prevent eivah.

Therefore, when R. Moshe (Igros Moshe O.C. 4:79) is matir nowadays chilul shabbos for the pikuach nefesh of goyim, he explains that eivah is not sufficient to permit it. R. Moshe permits it because the animosity will be so strong against Jews and will be so publicized in the media that it will lead to pikuach nefesh of a Jew - כפי המצב במדינותינו בזמן הזה איכא מצד איבה סכנה גדולה אף במדינות שהרשות לכל אדם מישראל להתנהג בדיני התורה וכו' ופלא על הגאון החפץ חיים (מ"ב ס' ש"ל ס"ק ח') שכתב דהא הרופאים אפילו היותר כשרים נוסעים כמה פרסאות לרפאות עכו"ם ושוחקין סממנים בעצמן, ומסיק דמחללי שבת גמורים הם במזיד אף שיהיה איבה מזה, הא ברוסלאנד בעיירות הקטנות שהיה רק רופא אחד לכל הסביבה הרי ודאי ברור אם לא היה הולך לרפאות את העכו"ם היה ברור שהיו הורגין אותו בטענתם שגרם מיתה לבנם ובתם וכו' ועיין בחת"ס חיו"ד ס' קל"א שכתב בפירוש ואם יש באיבה זו חשש סכנת נפשות יש להתיר אפילו מלאכה דאורייתא וכו' לכן פשוט שבזמננו יש לדון זה כסכנה ממש ויש להתיר כשנזדמן זה. This also enters into a realm of what qualifies as pikuach nefesh - since the individual who would be in sakana if we wouldn't save the goy cannot be identified (big discussion between the chazon ish y.d. 208:7 and nodeh b'yehuda regarding the hagdara of pikuach nefesh when there is no individual lying in front of you in need of being saved), it is more of a meta concern of sakana - וצריך עיון

Avoda Zara 25a - The Silence of the Sun

The pasuk refers to the stopping of time by the sun standing in place as the "silence" of the sun. Rashi offers a very insightful interpretation as to why the term "silence" is appropriate.

וידום - שתק מלומר שירה, שבכל עת לכתו אינו שותק, ובעמידתו שותק, ויהושע אומר שירה בשבילה דכתיב אז ידבר יהושע

Rashi explains that as the sun travels it sings, but the song of Yehoshua filled in for the sun to allow it to remain silent - to stand in place. What does this mean?

The concept of "shira" - song, is the fulfillment of the command of Hashem, confirming him as the creator and conductor of the world. As the sun travels from its rising to its setting, it is following the laws of nature set by Hashem, thereby publicly sanctifying the name of Hashem. "Shira" is the public kiddush Hashem - sanctification of Hashem's name. The sun cannot stop because there would be a necessary Kiddush Hashem missing in the world. However, when Yehoshua sings "shira" and publicly recognizes the hand of Hashem in the battles that he is fighting, the Kiddush Hashem of Yehoshua can replace that of the sun, thereby enabling the sun to stand still, in silence. Perhaps this will answer the question of Tosafos from Yaacov Avinu. The fact that the sun will rise early or set more quickly doesn't constitute a silence since it is still moving the entire time whether quickly or slowly. It is only when the sun literally stands still - ויעמוד השמש בחצי השמים ולא אץ לבא that there is a lack of "shira" which must be compensated for. That would also explain why by Chizkiyahu Tosafos writes that the sun went backwards, but couldn't stand in silence, unless there was a kiddush hashem of a major caliber to compensate for it.

Avoda Zara 23b - 24a - Kibud Av for a Goy - Dama Ben Nesina

I posted here about kibud av being a mitzvah for a goy also, although not one of the 7 mitzvos.

Another interesting point - Who's owned the precious stone and would have profited from the sale, the dama (son) or (nesina) father? If it were owned by the father it wouldn't make sense that the son "fulfilled" kibud av by not waking him. When a father demands that the son wake him or if the son is sure that the father would want to be woken (so that he can sell a diamond or go to minyan) it would be a violation of kibud av NOT to wake him. Therefore, if the stone was owned by the father, the refusal to wake him shouldn't be a fulfillment of kibud av, rather a violation. But, if the stone were owned by the son, why was he not allowed to wake the father - the din of kibud av for even a Jew is משל אב, meaning that it is at the fathers expense. Certainly the mitzvah for a goy would not extend beyond the requirement for a Jew, so the son would not have to incur a loss to avoid waking his father. How then can we learn from dama ben nesina עד היכן כיבוד אב ואם, if it were the father's stone he violated kibud av, if it were the son's stone he wasn't required to suffer a loss? From here we learn a fundamental distinction between a loss and a lack of profit. When we say that kibud av is משל אב, that means that the father must incur the loss if there is a loss of principal , but the son is obligated to incur a loss of profits because מניעת הריוח - loss of potential profits, doesn't qualify as a loss. This would also be the rationale for the Rosh who would require a son to miss work and lose that days profits in order to go help his father.

Avoda Zara 20a - Gifts to Goyim

The gemara says that one of the things that we learn out from the pasuk of לא תחנם is that one cannot offer goyim free gifts. Tosafos qualifies this based on the opinion of R. Yehuda himself in Pesachim who says that one can send a gift to a goy, that it is only prohibited if you don't know him. A goy that is a friend or neighbor can be given a gift because he will "owe" appreciation and do something in return so that every gift is essentially a sale. Tosafos then asks how can the mishna in gittin permit supporting goyim who are poor, it should be prohibited since the donor receives nothing in return. Tosafos explains that since it was instituted for the purpose of darkei shalom - maintaining peace, it is not considered a "free gift". Tosafos understands that darkei shalom is not only the reason to require it, it is also the rationale to permit it.

Being that in the context of a free gift לא תחנם doesn't prohibit gifts for the benefit of the Yisroel, the same should apply to the other aspect of לא תחנם, not giving them a place to live in Eretz Yisroel. Therefore, if a Jew is going to sell land in E.Y. for his own personal gain i.e. during the shemita year to exempt the land from kedushas shevi'is, it shouldn't violate לא תחנם. However, the Chazon Ish (Shevi'is 24:4) writes that this is not true. Although the aspect of free gift is permitted for the benefit of the Jew, that is because it no longer qualifies as a FREE gift and doesn't fit the definition of the prohibition. But, it would be forbidden to give them a place in the land of E.Y. even for the benefit of the Jew.

The Ran (end of perek 6b in Ri"f pages, end of mishna) cites a Yerushalmi that allows a Jew to rent land to a goy when there is no Yisroel interested in renting. Although there is a gezeira not o rent land in E.Y. to a goy because you may come to sell, it seems that since it is done for the benefit of the Jew it is permitted. This would contradict the Chazon Ish? The answer is fairly obvious. The Torah prohibition to sell would surely apply even if done for the benefit of the Jew, but the Rabbinic gezeira against renting to goyim was never meant to apply when there is significant loss to the Jew.

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On another note - there is a halacha that comes from Tosafos d.h. v'rebi meir, that is worthy of mentioning and being aware of. Tosafos holds that the obligation to give to a ger toshav before selling to a goy, should technically require every Jew to give to his fellow Jew before selling to a goy. Tosafos explains that it only applies to situations where the value to the Jew is very low, and to the receiver would be significant, but a person is not required to suffer a significant loss by gifting an item that he can sell. Based on this, if follows that if for example one has an option of hiring a Jew (or sell to a Jew) at a slightly higher cost than goy, he would be required to suffer a minor loss to hire or sell to the Jew.

Avoda Zara 19a - Learning To Remember

The gemara discusses learning styles such as learning superficially the entire Torah even at the expense of remembering and even at the expense of depth, and only afterward learning in-depth. Furthermore, the gemara points out that one should be a רמאי in the sense that he plans out his learning to enable the best retention and supports this with a parable of a bird trapper who breaks the wings after each capture (although it takes time to break the wings and he catches fewer birds, at least he will retain those that he captured).

The Shulchan Aruch of the Ba'al Ha'tanya (kunteros talmud torah chapter 2: 5-11) has an elaborate discussion about the prohibition to forget one's learning and when it applies. He explains that if one knows himself to forget very easily, their learning must be organized in a way that allows for the most review even at the expense of covering ground so that he doesn't forget what he has learned. He explains that we find even the chachamim of the talmud were sometimes experts in only one or two tractates, presumably because they were preoccupied with reviewing that they have learned and were unable to move on. A person like this must prioritize the areas that are practical so that if he leaves sections of Torah untouched, it will be the areas that are less practical. Most of his approach to limud ha'torah is very practical and rationale. The only exception is when he describes the type of individual who spends almost all his learning time on review so that he doesn't forget. This individual, if left with some extra time should use it to study the areas of Torah that he otherwise wouldn't get to, even if he will cover them only once and most likely completely forget what he has learned. Why?

כדי שיוכל ללמוד כל התורה שבעל פה כולה פעם אחד בחייו לקיים מצות "שמור תשמרון את כל המצוה" וכו' ואף שישכח הכל, הרי לעתיד לבוא יזכירוהו כל לימודו ששכח מחמת אנסו שאי אפשר לו לחזור כ"כ שלא ישכח לימוד זה שלומד רק שעה קטנה בכל יום, כי שאר היום והלילה צריך לו לחזור על לימוד המביא לידי מעשה וכו

Here he deviates from the practical and enters a more chassidic realm where he says that the entire Torah should be covered at least once in a persons lifetime, even if there will be no retention (but of course the large majority of his time and energy should be invested in reviewing the areas that he will remember).