In mathematics, an **-algebra** in a symmetric monoidal infinity category *C* consists of the following data:

- An object for any open subset
*U*of**R**^{n}homeomorphic to an*n*-disk. - A multiplication map:

- for any disjoint open disks contained in some open disk
*V*

subject to the requirements that the multiplication maps are compatible with composition, and that is an equivalence if . An equivalent definition is that *A* is an algebra in *C* over the little *n*-disks operad.

- An -algebra in vector spaces over a field is a unital associative algebra if
*n*= 1, and a unital commutative associative algebra if*n*≥ 2.^{[ citation needed ]} - An -algebra in categories is a monoidal category if
*n*= 1 , a braided monoidal category if*n*= 2, and a symmetric monoidal category if*n*≥ 3. - If Λ is a commutative ring, then defines an -algebra in the infinity category of chain complexes of -modules.

In mathematics, a **Hopf algebra**, named after Heinz Hopf, is a structure that is simultaneously an algebra and a coalgebra, with these structures' compatibility making it a bialgebra, and that moreover is equipped with an antiautomorphism satisfying a certain property. The representation theory of a Hopf algebra is particularly nice, since the existence of compatible comultiplication, counit, and antipode allows for the construction of tensor products of representations, trivial representations, and dual representations.

In mathematics, a **monoidal category** is a category equipped with a bifunctor

In mathematics and theoretical physics, the term **quantum group** denotes one of a few different kinds of noncommutative algebras with additional structure. These include Drinfeld–Jimbo type quantum groups, compact matrix quantum groups, and bicrossproduct quantum groups.

In category theory, a branch of mathematics, a **monad** is an endofunctor, together with two natural transformations required to fulfill certain coherence conditions. Monads are used in the theory of pairs of adjoint functors, and they generalize closure operators on partially ordered sets to arbitrary categories.

In mathematics and theoretical physics, a **superalgebra** is a **Z**_{2}-graded algebra. That is, it is an algebra over a commutative ring or field with a decomposition into "even" and "odd" pieces and a multiplication operator that respects the grading.

In mathematics, a *commutativity constraint* on a monoidal category * is a choice of isomorphism for each pair of objects **A* and *B* which form a "natural family." In particular, to have a commutativity constraint, one must have for all pairs of objects .

In mathematics, **categorification** is the process of replacing set-theoretic theorems with category-theoretic analogues. Categorification, when done successfully, replaces sets with categories, functions with functors, and equations with natural isomorphisms of functors satisfying additional properties. The term was coined by Louis Crane.

In mathematics, especially in the fields of representation theory and module theory, a **Frobenius algebra** is a finite-dimensional unital associative algebra with a special kind of bilinear form which gives the algebras particularly nice duality theories. Frobenius algebras began to be studied in the 1930s by Richard Brauer and Cecil Nesbitt and were named after Ferdinand Frobenius. Tadashi Nakayama discovered the beginnings of a rich duality theory, . Jean Dieudonné used this to characterize Frobenius algebras. Frobenius algebras were generalized to quasi-Frobenius rings, those Noetherian rings whose right regular representation is injective. In recent times, interest has been renewed in Frobenius algebras due to connections to topological quantum field theory.

In mathematics, an **operad** is concerned with prototypical algebras that model properties such as commutativity or anticommutativity as well as various amounts of associativity. Operads generalize the various associativity properties already observed in algebras and coalgebras such as Lie algebras or Poisson algebras by modeling computational trees within the algebra. Algebras are to operads as group representations are to groups. An operad can be seen as a set of operations, each one having a fixed finite number of inputs (arguments) and one output, which can be composed one with others. They form a category-theoretic analog of universal algebra.

In mathematics, a **Hirzebruch surface** is a ruled surface over the projective line. They were studied by Friedrich Hirzebruch (1951).

In category theory, monoidal functors are functors between monoidal categories which preserve the monoidal structure. More specifically, a monoidal functor between two monoidal categories consists of a functor between the categories, along with two *coherence maps*—a natural transformation and a morphism that preserve monoidal multiplication and unit, respectively. Mathematicians require these coherence maps to satisfy additional properties depending on how strictly they want to preserve the monoidal structure; each of these properties gives rise to a slightly different definition of monoidal functors

In category theory, a **monoidal monad** is a monad on a monoidal category such that the functor is a lax monoidal functor and the natural transformations and are monoidal natural transformations. In other words, is equipped with coherence maps and satisfying certain properties, and the unit and multiplication are monoidal natural transformations. By monoidality of , the morphisms and are necessarily equal.

In category theory, a branch of mathematics, a **PROP** is a symmetric strict monoidal category whose objects are the natural numbers *n* identified with the finite sets and whose tensor product is given on objects by the addition on numbers. Because of “symmetric”, for each *n*, the symmetric group on *n* letters is given as a subgroup of the automorphism group of *n*. The name PROP is an abbreviation of "PROduct and Permutation category".

In mathematics, the **Hall algebra** is an associative algebra with a basis corresponding to isomorphism classes of finite abelian *p*-groups. It was first discussed by Steinitz (1901) but forgotten until it was rediscovered by Philip Hall (1959), both of whom published no more than brief summaries of their work. The **Hall polynomials** are the structure constants of the **Hall algebra**. The Hall algebra plays an important role in the theory of Masaki Kashiwara and George Lusztig regarding canonical bases in quantum groups. Ringel (1990) generalized Hall algebras to more general categories, such as the category of representations of a quiver.

In category theory, a branch of mathematics, the **center** is a variant of the notion of the center of a monoid, group, or ring to a category.

In mathematics, a **Bose–Mesner algebra** is a special set of matrices which arise from a combinatorial structure known as an association scheme, together with the usual set of rules for combining those matrices, such that they form an associative algebra, or, more precisely, a unitary commutative algebra. Among these rules are:

In mathematics, a **highly structured ring spectrum** or -ring is an object in homotopy theory encoding a refinement of a multiplicative structure on a cohomology theory. A commutative version of an -ring is called an -ring. While originally motivated by questions of geometric topology and bundle theory, they are today most often used in stable homotopy theory.

A **Lie conformal algebra** is in some sense a generalization of a Lie algebra in that it too is a "Lie algebra," though in a different pseudo-tensor category. Lie conformal algebras are very closely related to vertex algebras and have many applications in other areas of algebra and integrable systems.

In algebra, a **λ-ring** or **lambda ring** is a commutative ring together with some operations λ^{n} on it that behave like the exterior powers of vector spaces. Many rings considered in K-theory carry a natural λ-ring structure. λ-rings also provide a powerful formalism for studying an action of the symmetric functions on the ring of polynomials, recovering and extending many classical results.

A **coherent algebra** is an algebra of complex square matrices that is closed under ordinary matrix multiplication, Schur product, transposition, and contains both the identity matrix and the all-ones matrix .

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