Gemara Shabbos says that originally one was allowed to bathe on Shabbos in pre-heated bath-houses. However, (in short) due to the fact that the bath-house directors would violate Shabbos (by heating ...
The Bavli, Shabas 7 amud 2, has a discussion about holes in walls, where things might land if thrown. Holes on the r'shus-hayachid-facing side of a wall are deemed r'shus hayachid, so tossing ...
The Gemara in Shabbos says that Bibi bar Abaye asks if one can violate a Rabbinic commandment (unsticking a loaf from an oven) to save oneself from being "chayav a chattas". The Gemara says that ...