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
Kronecker symbol Kronecker symbol In number theory, the Kronecker symbol, written as formula_1 or formula_2, is a generalization of the Jacobi symbol to all integers formula_3. It was introduced by . Let formula_3 be a non-zero integer, with prime factorization where formula_6 is a unit (i.e., formula_7), and the formula_8 are primes. Let formula_9 be an integer. The Kronecker symbol formula_10 is defined by For odd formula_8, the number formula_13 is simply the usual Legendre symbol. This leaves the case when formula_14. We define formula_15 by Since it extends the Jacobi symbol, the quantity formula_17 is simply formula_18 when formula_19. When formula_20,