Finite Thickness

In formal language theory, a class of languages has finite thickness if for every string s, there are only finitely many consistent languages in . This condition was introduced by Dana Angluin in connection with learning, as a sufficient condition for language identification in the limit. The related notion of M-finite thickness

We say that satisfies the MEF-condition if for each string s and each consistent language L in the class, there is a minimal consistent language in, which is a sublanguage of L. Symmetrically, we say that satisfies the MFF-condition if for every string s there are only finitely many minimal consistent languages in . Finally, is said to have M-finite thickness if it satisfies both the MEF and MFF conditions.

Finite thickness implies M-finite thickness. However, there are classes that are of M-finite thickness but not of finite thickness (for example, let be a class of languages such that ).