László Babai

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A simple parallel randomized algorithm to find a maximal independent set in a graph G = (V, E) on n vertices is presented. Its expected rmming time on a concurrent-read concurrent-write PRAM with 0( 1 E 1 d,,) processors is O(log n), where d,, denotes the maximum degree. On an exclusive-read exclusive-write PRAM with 0( 1 El) processors the algorithm runs(More)
We determine the exact power of two-prover interactive proof systems introduced by Ben-Or, Goldwasser, Kilian, and Wigderson (1988). In this system, two all-powerful noncommunicating provers convince a randomizing polynomial time verifier in polynomial time that the inputx belongs to the languageL. We show that the class of languages having tow-prover(More)
In a previous paper [BS] we proved, using the elements of the theory of <italic>nilpotent groups</italic>, that some of the <italic>fundamental computational problems in matriz groups</italic> belong to <italic>NP</italic>. These problems were also shown to belong to <italic>coNP</italic>, assuming an <italic>unproven hypothesis</italic> concerning(More)
We take a complexity theoretic view of A. C. Yao's theory of communication complexity. A rich structure of natural complexity classes is introduced. Besides providing a more structured approach to the complexity of a variety of concrete problems of interest to VLSI, the main objective is to exploit the analogy between Turing machine (TM) and communication(More)
Motivated by Manuel Blum’s concept of inst ante checking, we consider new, very fast and generic mechanisms of checking computations. Our results exploit recent advances in interactive proof protocols [LFKN], [Sh], and especially the MIP = NEXP protocol from [BFL]. WJe show that every nondeterministic computational task S(Z, y), defined as a polynomial time(More)
Let f (xl, .. . xk) be a Boolean function that k parties wish to collaboratively evaluate, where each xi is a bit-string of length n. The ith party knows each input argument except x,; and each party has unlimited computational power. They share a blackboard, viewed by all parties, where they can exchange messages. The objective is to minimize the number of(More)
We announce an algebraic approach to the problem of assigning <italic>canonical forms</italic> to graphs. We compute canonical forms and the associated canonical labelings (or renumberings) in polynomial time for graphs of bounded valence, in moderately exponential, exp(n<supscrpt>&#189; + &ogr;(1)</supscrpt>),time for general graphs, in subexponential,(More)
We show thatBPP can be simulated in subexponential time for infinitely many input lengths unless exponential time ℴ collapses to the second level of the polynomial-time hierarchy. ℴ has polynomial-size circuits and ℴ has publishable proofs (EXPTIME=MA). ℴ collapses to the second level of the polynomial-time hierarchy. ℴ has polynomial-size circuits and ℴ(More)