Book excerpt: Connecting these puzzle cells involves using your brain cells to the max! Masyu features a series of black and white circles arranged in a grid; the object is to join them in a single, unbroken loop with a line that passes through every circle. Of course, there s a twist: there are special rules about how the line may make 90-degree turns when it passes through a black or a white circle. It s like a maze with no walls, and there s only one solutiontry to find it! In addition to the 90 masyu, there are 45 sudoku, too."