Abstract
This paper studies the class ofinfinite sets that have minimal perfect hash functions—one-to-one onto maps between the sets and ∑*-computable in polynomial time. We will call such sets P-compressible. We show that all standard NP-complete sets are P-compressible, and give a structural condition,E = ∑ E2 , sufficient to ensure thatall infinite NP sets are P-compressible. On the other hand, we present evidence that some infinite NP sets, and indeed some infinite P sets, are not P-compressible: if an infinite NP setA is P-compressible, thenA has an infinite sparse NP subset, yet we construct a relativized world in which some infinite NP sets lack infinite sparse NP subsets. This world is built upon a result that is of interest in its own right; we determine optimally—with respect to any relativizable proof technique—the complexity of the easiest infinite sparse subsets that infinite P sets are guaranteed to have.
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Goldsmith, J., Kunen, K. & Hemachandra, L.A. Polynomial-time compression. Comput Complexity 2, 18–39 (1992). https://doi.org/10.1007/BF01276437
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DOI: https://doi.org/10.1007/BF01276437