Infinity symbol in bookbinding to indicate that a book is printed on acid-free paper and will therefore be long-lasting. In modern mysticism, the infinity symbol has become identified with a variation of the ouroboros, an ancient image of a snake eating its own tail that has also come to symbolize the infinite, and the ouroboros is sometimes drawn in figure-eight form to reflect this identification, rather than in its more traditional circular form. In the works of Vladimir Nabokov, including "The Gift" and "Pale Fire", the figure-eight shape is used symbolically to refer to the Möbius strip and the infinite, for instance
Recycling symbol (U+2678), ♹ (U+2679), and ♺ (U+267A). Recycling codes extend these numbers above 7 to include various non-plastic materials, including metals, glass, paper, and batteries of various types. ♾, an infinity sign (∞) inside a circle, represents the permanent paper symbol, used in packaging and publishing to signify the use of durable acid-free paper. In some ways, this logo expresses the "opposite" intention from the recycle logo, in that the acid-free paper is intended to last indefinitely, rather than being recycled. Nevertheless, acid-free paper does not usually contain toxic materials (although certain inks do), so it is easily recycled or composted.