This chapter introduces Turing machine as a computing model and defines computability and decidability. It is shown that some decision problems are undecidable by Cantor’s diagonal method and reduction, and an infinite set is computable (i.e., recognizable) if and only if the set has a computable bijection with the set of natural numbers. The chapter concludes with some undecidable first-order logic problems.

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Decidable and Undecidable Problems

  • Hantao Zhang,
  • Jian Zhang

摘要

This chapter introduces Turing machine as a computing model and defines computability and decidability. It is shown that some decision problems are undecidable by Cantor’s diagonal method and reduction, and an infinite set is computable (i.e., recognizable) if and only if the set has a computable bijection with the set of natural numbers. The chapter concludes with some undecidable first-order logic problems.