Research output: Contribution to journal › Article › peer-review
On language equations with concatenation and various sets of boolean operations. / Okhotin, Alexander.
In: RAIRO - Theoretical Informatics and Applications, Vol. 49, No. 3, 01.07.2015, p. 205-232.Research output: Contribution to journal › Article › peer-review
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TY - JOUR
T1 - On language equations with concatenation and various sets of boolean operations
AU - Okhotin, Alexander
PY - 2015/7/1
Y1 - 2015/7/1
N2 - Systems of equations of the form Xi = ℓi(X1, . . .,Xn), for 1 ≤i ≤ n, in which the unknowns Xi are formal languages, and the right-hand sides ≤i may contain concatenation and union, are known for representing context-free grammars. If, instead of union only, another set of Boolean operations is used, the expressive power of such equations may change: for example, using both union and intersection leads to conjunctive grammars [A. Okhotin, J. Automata, Languages and Combinatorics 6 (2001) 519-535], whereas using all Boolean operations allows all recursive sets to be expressed by unique solutions [A. Okhotin, Decision problems for language equations with Boolean operations, Automata, Languages and Programming, ICALP 2003, Eindhoven, The Netherlands, 239-251]. This paper investigates the expressive power of such equations with any possible set of Boolean operations. It is determined that different sets of Boolean operations give rise to exactly seven families of formal languages: the recursive languages, the conjunctive languages, the context-free languages, a certain family incomparable with the context-free languages, as well as three subregular families.
AB - Systems of equations of the form Xi = ℓi(X1, . . .,Xn), for 1 ≤i ≤ n, in which the unknowns Xi are formal languages, and the right-hand sides ≤i may contain concatenation and union, are known for representing context-free grammars. If, instead of union only, another set of Boolean operations is used, the expressive power of such equations may change: for example, using both union and intersection leads to conjunctive grammars [A. Okhotin, J. Automata, Languages and Combinatorics 6 (2001) 519-535], whereas using all Boolean operations allows all recursive sets to be expressed by unique solutions [A. Okhotin, Decision problems for language equations with Boolean operations, Automata, Languages and Programming, ICALP 2003, Eindhoven, The Netherlands, 239-251]. This paper investigates the expressive power of such equations with any possible set of Boolean operations. It is determined that different sets of Boolean operations give rise to exactly seven families of formal languages: the recursive languages, the conjunctive languages, the context-free languages, a certain family incomparable with the context-free languages, as well as three subregular families.
UR - http://www.scopus.com/inward/record.url?scp=85006833233&partnerID=8YFLogxK
U2 - 10.1051/ita/2015006
DO - 10.1051/ita/2015006
M3 - Article
AN - SCOPUS:85006833233
VL - 49
SP - 205
EP - 232
JO - RAIRO - Theoretical Informatics and Applications
JF - RAIRO - Theoretical Informatics and Applications
SN - 0988-3754
IS - 3
ER -
ID: 41137800