Projective Hierarchy

Projective Hierarchy

In the mathematical field of descriptive set theory, a subset of a Polish space is projective if it is for some positive integer . Here is

  • if is analytic
  • if the complement of, is
  • if there is a Polish space and a subset such that is the projection of ; that is,

The choice of the Polish space in the third clause above is not very important; it could be replaced in the definition by a fixed uncountable Polish space, say Baire space or Cantor space or the real line.

Read more about Projective Hierarchy:  Relationship To The Analytical Hierarchy

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