Lecture Notes in Computer Science Volume 4393, 2007, pp 500-511

Languages with Bounded Multiparty Communication Complexity

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We study languages with bounded communication complexity in the multiparty “input on the forehead model” with worst-case partition. In the two-party case, languages with bounded complexity are exactly those recognized by programs over commutative monoids [19]. This can be used to show that these languages all lie in shallow ACC0.

In contrast, we use coding techniques to show that there are languages of arbitrarily large circuit complexity which can be recognized in constant communication by k players for k ≥ 3. However, we show that if a language has a neutral letter and bounded communication complexity in the k-party game for some fixed k then the language is in fact regular. We give an algebraic characterization of regular languages with this property. We also prove that a symmetric language has bounded k-party complexity for some fixed k iff it has bounded two party complexity.

Supported in part by the NSF (M. Szegedy), NSERC (A. Chattopadhyay, P. Tesson, D. Thérien), FQRNT (D. Thérien), grant GA-CR 201/05/0124, ITI-1M0545 (M. Koucký) and the A.V. Humboldt Foundation (P. Tesson and D. Thérien). We thank Pavel Pudlák for suggesting the use of the Hales-Jewett Theorem.