The 2 diagrams above show the basic premise. However, it gets very sophisticated.
1. Plus and minus signs: A plus sign may have a 4 on it. That means, if your purple ribbon goes over it, its length will increase by that amount.
2. The X. A ribbon can land on it, but that's where it must end. Some levels have an equal number of X's as ribbons. But not all.
3.The side portals: They act like wormholes, but they're always on the outer edges of the puzzles.
There are 400 levels, which is way too many. At the moment, I've solved about 100 levels at various levels of difficulty, including 'insane'.
At the moment, I've solved about 40 levels.