Concept
Arf invariant
Concepts associés (4)
Signature (topology)
In the field of topology, the signature is an integer invariant which is defined for an oriented manifold M of dimension divisible by four. This invariant of a manifold has been studied in detail, starting with Rokhlin's theorem for 4-manifolds, and Hirzebruch signature theorem. Given a connected and oriented manifold M of dimension 4k, the cup product gives rise to a quadratic form Q on the 'middle' real cohomology group The basic identity for the cup product shows that with p = q = 2k the product is symmetric.
Ε-quadratic form
In mathematics, specifically the theory of quadratic forms, an ε-quadratic form is a generalization of quadratic forms to skew-symmetric settings and to *-rings; ε = ±1, accordingly for symmetric or skew-symmetric. They are also called -quadratic forms, particularly in the context of surgery theory. There is the related notion of ε-symmetric forms, which generalizes symmetric forms, skew-symmetric forms (= symplectic forms), Hermitian forms, and skew-Hermitian forms.
Singly and doubly even
In mathematics an even integer, that is, a number that is divisible by 2, is called evenly even or doubly even if it is a multiple of 4, and oddly even or singly even if it is not. The former names are traditional ones, derived from ancient Greek mathematics; the latter have become common in recent decades. These names reflect a basic concept in number theory, the 2-order of an integer: how many times the integer can be divided by 2. This is equivalent to the multiplicity of 2 in the prime factorization.
L-théorie algébrique
En mathématiques, la « L-théorie algébrique » est l'équivalent de la K -théorie pour des formes quadratiques. Le terme a été inventé par C. T. C. Wall, qui a utilisé L car c'était la lettre après le K . La théorie L algébrique, également connue sous le nom de « théorie K hermitienne », est importante dans la théorie de la chirurgie. On peut définir des L -groupes pour tout anneau d'involution R : les L -groupes quadratiques (Wall) et les L -groupes symétriques (Mishchenko, Ranicki).