You know what, the game loop is simple but I had an absolute blast!
The inversions really ramps up the difficulty, I think you could probably smooth out the difficulty curve by introducing new concepts (double possession, triple possession, inversions etc) on new days.
Also the Esc button instantly yanking me to desktop without a confirmation threw me off when trying to close the book.
Very minor criticisms of an otherwise rather good little game! Bravo!