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\begin{document}

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\section*{algebraic structure}

Algebraic structure may mean either

\begin{itemize}%
\item the same as [[algebra]] in the sense of [[universal algebra]];

\end{itemize}
or

\begin{itemize}%
\item the [[extra structure]] which such an algebra has with respect to the underlying object.

\end{itemize}
There are several notions of an \textbf{algebraic structure} on an object of some category or higher category, which differ in generality. It may be to be an algebra over an [[algebraic theory]], [[algebra over an operad]] (or higher operad) or an [[algebra over a monad]], or over a [[PROP]], over a [[properad]] etc. See also [[variety of algebras]].

There is also an older notion of an algebraic structure/algebra as a model for a one-sorted [[theory]] where the only relation symbols in the language involved are $\epsilon$ and equality (with standard interpretation in models). This notion includes for example fields which are not an algebraic theory in the sense of monads (because there are no free objects in the case of fields, i.e. the category of fields is not [[monadic functor|monadic]] over the category of sets).

There is a [[forgetful functor]] from the category of algebras/algebraic structures of some type (in any of the above formalisms) to the original category. This functor \textbf{forgets structure} in the sense of [[stuff, structure, property]]. We say that a functor in the base category \textbf{preserves some algebraic structure} if it lifts to the corresponding category of algebras.

[[!redirects algebraic structures]]



\end{document}