groupoid
Noun
Meaning
(algebra) A magma: a set with a total binary operation.
(algebra and category theory) A set with a partial binary operation that is associative and has identities and inverses.
Source: en.wiktionary.orgExamples
A groupoid is a category in which every morphism is an isomorphism.
A groupoid can be seen as a: * Group with a partial function replacing the binary operation ; * Category in which every morphism is invertible.
Examples Linear algebra Given a field K, the corresponding general linear groupoid GL * (K) consists of all invertible matrices whose entries range over K. Matrix multiplication interprets composition.
Further the stabilizers of the action are the vertex groups, and the orbits of the action are the components, of the action groupoid.
Category of groupoids A subgroupoid is a subcategory that is itself a groupoid.
Given a groupoid in the category-theoretic sense, let G be the disjoint union of all of the sets G(x,y) (i.e. the sets of morphisms from x to y).