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In mathematics, quasi-bialgebras are a generalization of bialgebras: they were first defined by the Ukrainian mathematician Vladimir Drinfeld in 1990. A quasi-bialgebra differs from a bialgebra by having coassociativity replaced by an invertible element which controls the non-coassociativity. One of their key properties is that the corresponding category of modules forms a tensor category. == Definition == A quasi-bialgebra is an algebra over a field equipped with morphisms of algebras : : along with invertible elements , and such that the following identities hold: : : : : Where and are called the comultiplication and counit, and are called the right and left unit constraints (resp.), and is sometimes called the ''Drinfeld associator''.〔C. Kassel. "Quantum Groups". Graduate Texts in Mathematics Springer-Verlag. ISBN 0387943706〕 This definition is constructed so that the category is a tensor category under the usual vector space tensor product, and in fact this can be taken as the definition instead of the list of above identities.〔 Since many of the quasi-bialgebras that appear "in nature" have trivial unit constraints, ie. the definition may sometimes be given with this assumed.〔 Note that a bialgebra is just a quasi-bialgebra with trivial unit and associativity constraints: and . 抄文引用元・出典: フリー百科事典『 ウィキペディア(Wikipedia)』 ■ウィキペディアで「Quasi-bialgebra」の詳細全文を読む スポンサード リンク
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