Stop the lines crossing over by moving the balls around. Once you finish a level you can click to start the next level with one more ball.
https://en.wikipedia.org/wiki/Planarity Ideas to mess around with: * Add a timer, and record best times per level. * Make it harder by having the dots drift around on their own. * Restrict dot positions to a predefined set of points, and have the solutions be actual pictures. Perhaps as part of a background image. * Use different algorithms to generate problems.
