Four glasses are in a row right side up.
In each move, you must invert exactly 3 different glasses. Invert means to flip a glass, so a right side up glass it turned upside down, and vice versa. Find, with proof, the minimum number of moves so that all glasses are turned upside down.
What if there are n glasses, and you have to invert n – 1 glasses at a time? For which n is there a solution, and what is the minimum number of moves?
