"Chi" is made up of two lines crossing each other as in the shape of an "X". The line that starts leftmost on top, comes down, and is rightmost on the bottom, and vice versa. If one thinks of the lines as concepts, one sees that concept A, which comes first, is also last, and concept B, which comes after A, comes before A. If one adds in more lines representing other concepts, one gets a chiastic structure with more concepts.