Aside from lower left I was able to figure out the puzzles without too much difficulty. The book riddles were thankfully not hard to decipher. In general I think repressing the key to show something should hide it. Opening the books seem to darken the screen a little, but it adds on top of every you press a book key before closing turning the rest of the screen black; when I tried to close a book by repressing the F key I thought I was activating a screen darkening function for a moment. Great job for a first game!