- 一般社団法人 日本応用数理学会
- 応用数理 (ISSN:24321982)
- vol.31, no.4, pp.15-22, 2021-12-22 (Released:2022-03-31)
Formal language theory is the field of study of non-commutative objects so-called “languages” (sets of words). While many problems on languages are difficult to solve due to the non-commutativity, the situation could be drastically changed if we consider a commutative invariant of a language. This paper explains some commutative invariants of languages with concrete examples.