DECIDABILITY OF REGULAR LANGUAGE GENUS COMPUTATION

Guillaume Bonfante (1) , Florian Deloup (2)

1 CARBONE - Carbone
2 IMT - Institut de Mathématiques de Toulouse UMR5219

The article continues the study of the genus of regular languages that the authors introduced in a 2012 paper. Let L be a regular language. In order to understand the genus g(L) of L, we introduce the topological size of |L|top to be the minimal size of all finite deterministic automata of genus g(L) computing L. We show that the minimal finite deterministic automaton of a regular language can be arbitrary far away from a finite deterministic automaton realizing the minimal genus and computing the same language, both in terms of the difference of genera and in terms of the difference in size. We show that the topological size |L|top can grow at least exponentially in size |L|. We conjecture the genus of every regular language to be computable. This conjecture implies in particular that the planarity of a regular language is decidable, a question asked in 1978 by R.V. Book and A.K. Chandra. We prove here the conjecture for a fairly generic class of regular languages having no short cycles.

Domaines: Complexité [cs.CC]

Guillaume Bonfante, Florian Deloup. DECIDABILITY OF REGULAR LANGUAGE GENUS COMPUTATION. Mathematical Structures in Computer Science, 2019, 29 (9), pp.1428-1443. ⟨10.1017/S0960129519000057⟩. ⟨hal-03178810⟩