An EXPSPACE Lower Bound
Albert Meyer, in the first decade of his career, was one of the top theorists in the world, yet you may not know his work in detail. The cause, most likely, is that years ago he closed down his research program in complexity theory, moving into the area of the logic and semantics of programming languages. While he was a complexity theorist, he helped invent the polynomial time hierarchy, he proved lower bounds on real-time Turing Machines, he showed huge lower bounds on various logical theories, he proved the sharpest nondeterministic time hierarchy theorem known, and more. Much of this was joint work with some of the best of the best: Mike Fischer, Mike Paterson, Charlie Rackoff, Larry Stockmeyer, and others.
KeywordsWord Problem Commutative Semigroup Reachability Problem Counter Machine Abelian Semigroup
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