Understanding "פסיק רישא דלא ניחא ליה" (inevitable results from one's permissible action whereby one receives no benefit from).
Reopening a Hole in the Ground That Was There from Before Shabbos;
How to work with shelving on bookcases and refrigerators.
Gathering Together Fruits in Various Ways (e.g., Kicking, Rolling, Sweeping) and Picking Up One at a Time;