תנא אמר הלה זייתי אני נוטל אין שומעיו לו- ב"מ ק"א

What about if the owner of the field doesn't want the olive trees in his field? Can he force the tree owner to uproot them? Or do we say he can't because of ישוב א"י? The Ritva writes that the owner of the field can force the owner of the trees to uproot them even in ארץ ישראל and this is brought down להלכה in שו"ע ח"מ סי' קס"ח. However, the Acharonim point out that this is really a machlokes the Rambam and the Raavad (הל' גזילה י,ה). The Rambam writes:

היורד לתוך שדה חברו שלא ברשות, ונטעה--אם הייתה שדה העשויה ליטע--אומדין כמה אדם רוצה ליתן בשדה זו ליטעה, ונוטל מבעל השדה; ואם אינה עשויה ליטע--שמין לו, וידו על התחתונה.
אמר לו בעל השדה, עקור אילנך ולך--שומעין לו

The Rambam writes that the owner of the field can force him to remove the trees. The Raavad there is משיג that this is in חו"ל but in א"י he is not allowed to uproot them because of ישוב א"י.

96b meisa machmas melacha vs. regular oness

What is the basis for the chiluk between meisa machmas melacha and a regular oness where even the animal dropping dead from a heart attack would be mechayev you?
Ramban calls it peshiya of the mashil -- that the mashil did not verify that the animal is up to the task he is lending it for. Rashba says, since "לאו לאוקמה בכילתא שאילתא" and he realizes that the animal will have wear and tear from the work and yet he does not set up an evaluation of the animal's worth, it shows he is not makpid. And once he is not makpid on כחש, he is not makpid on death either מחמת מלאכה, because of the idea of מה לי קטלה כולה מה לי קטלה פלגא

be'alav imo for city employees

Rav Meir explained today that according to rashi the teacher and barber are considered be'alav imo when they do melacha for you even though you are not paying them since they collect their salary from the city. In the previous lines, we were not paying the guy to give us a drink of water, so why is this a chiddush?
First of all, we see that Rishonim attack Rashi for his peshat and Ramban and others explain that the case is that these workers, since they are collecting their salary from all the inhabitants of the city, they are considered be'alav imo for everyone at all times, even when he is not teaching your son.
The shita suggests that the Ramban's peshat works in the words of Rashi as well.
Another possibility may be not to focus on the money but to say that the worker is not really working for you -- he works for the city and that is the chiddush.

בעל בנכסי אשתו (Bava Metzia 96a)

The Gemara has a question what is the status of the בעל with respect to the נכסי מלוג. What about the reverse? What is the status of the wife when she uses the husbands property?

The Ramabm (אישות כ"א:ט) writes:

האישה ששברה כלים, בעת שעושה מלאכותיה בתוך ביתה--פטורה: ואין זה מן הדין, אלא תקנה, שאם אין אתה אומר כן, אין שלום בתוך הבית לעולם--אלא נמצאת נזהרת ונמנעת מרוב המלאכות, ונמצאת קטטה ביניהם.

The ראב"ד there is משיג that the פטור is because of שאילה בבעלים. The ראב"ד seems to assume that just like the Gemara says that the husband with respect to the wifes property would be שאילה בבעלים (except that למסקנה he is a לוקח not a שואל), so too the reverse. The husband is משועבד to the wife and therefore it is always considered שאילה בבעלים. The Rambam would seem to assume that since the husband is not always working for the wife the פטור would not apply in all situations.

פועל משלו הוא אוכל (Bava Metzia 92a)

The Gemara says that the נ"מ is whether or not he can give to his wife and children. The Tur raises the question, what about if he picks it up to eat himself and then decides to give it to his wife or children (even if משמים הוא אוכל)? The Tur has 2 opinions and rejects the opinion that it is permitted. The Gra on Shulchan Aruch says that the 2 opinions are based on a machlokes Rashi and Tosafos. Rashi says "כל זמן דלא מטי לידיה לא זכי ליה". The implication is that once he does pick it up it his to do what he wants with including giving to his wife and kids. Tosafos however, says that he is not זוכה until he is "לועס ואוכל" which means that he cannot give it to his wife and kids.

In truth, Rashi on ד"ה אינו קוצץ) עמוד ב ) seems to say like Tosafos "דאין לפועל קטן זכות אלא שנותן לתוך פיו"

Also, in truth, Tosafos is a bit of a פלא, why should he only be זוכה when he puts it in his mouth? Why should this be different then any other מתנות עניים?

אתנן אסרה תורה (Bava Metzia 91a)

The way we have the גירסא the מסקנה is that there is no חיוב that ב"ד can impose because of קם ליה בדרבה מיניה however there is a חיוב בבא לצאת ידי שמים.

The מאירי in בבא קמא quotes a number of Rishonim who have a different גירסא in the Gemara and come to the opposite conclusion. They learn that both by אתנן and חסימה there is a חיוב to pay that ב"ד can enforce. What happened to קם ליה בדרבה מיניה? They learn that קם ליה בדרבה מיניה does not apply to a התחייבות מדעת. It only applies to a חיוב that is based on an action not a person's דעת. It comes out that according to these Rishonim by חסימה you would not say קם ליה בדרבה מיניה because the renter of the פרה agreed to the חיוב מדעת.

חסמה בקול (Bava Metzia 90b)

The simple understanding of the Gemara is like Rashi that he causes the animal not to eat by his voice by yelling at the animal when it is about to eat.

However, if you look carefully at Tosafos (ד"ה רבי יוחנן), you will see that Tosafos disagrees. Tosafos is bothered by a question that רבי יוחנן himself holds that עקימת שפתיו is not a מעשה by נשבע מימר ומקלל and therefore what is the חילוק here and why should חסימה בקול be חייב? Tosafos answers that here he is causing the animal to be דש with his voice and therefore בדיבוריה קא עביד מעשה. Tosafos learns pshat in חסמה בקול that he muzzled the animal normally and then with his voice caused the animal to be דש. This is very difficult in the words of the Gemara, according to Tosafos the Gemara should have asked דשה בקול. He wasn't חוסם בקול here at all. Tosafos is forced into this pshat because they need his דיבור to actually do something, cause the עבירה to happen. By לא תחסם the עיקר עבירה is the דישה while the animal is muzzled and therefore they had to learn that his דיבור caused the דישה.