Abstract family of languages

In computer science, in particular in the field of formal language theory, the term abstract family of languages refers to an abstract mathematical notion generalizing characteristics common to the regular languages, the context-free languages and the recursively enumerable languages, and other families of formal languages studied in the scientific literature.

A formal language is a set L for which there exists a finite set of abstract symbols Σ such that ${\displaystyle L\subseteq \Sigma ^{*}}$, where * is the Kleene star operation.

A family of languages is an ordered pair ${\displaystyle (\Sigma ,\Lambda )}$, where

A trio is a family of languages closed under e-free homomorphism, inverse homomorphism, and intersection with regular language.

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