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# analytic hierarchy

The *analytic hierarchy* is a hierarchy of either (depending on context) formulas or relations similar to the arithmetical hierarchy. It is essentially the second order equivalent. Like the arithmetical hierarchy, the relations in each level are exactly the relations defined by the formulas of that level.

The first level can be called $\Delta^{1}_{0}$, $\Delta^{1}_{1}$, $\Sigma^{1}_{0}$, or $\Pi^{1}_{0}$, and consists of the arithmetical formulas or relations.

A formula $\phi$ is $\Sigma^{1}_{n}$ if there is some arithmetical formula $\psi$ such that:

$\phi(\vec{k})=\exists X_{1}\forall X_{2}\cdots QX_{n}\psi(\vec{k},\vec{X}_{n})$ |

$\text{ where }Q\text{ is either }\forall\text{ or }\exists\text{, whichever % maintains the pattern of alternating quantifiers, and each }X_{i}\text{ is a % set variable (that is, second order)}$ |

Similarly, a formula $\phi$ is $\Pi^{1}_{n}$ if there is some arithmetical formula $\psi$ such that:

$\phi(\vec{k})=\forall X_{1}\exists X_{2}\cdots QX_{n}\psi(\vec{k},\vec{X}_{n})$ |

$\text{ where }Q\text{ is either }\forall\text{ or }\exists\text{, whichever % maintains the pattern of alternating quantifiers, and each }X_{i}\text{ is a % set variable (that is, second order)}$ |

Related:

ArithmeticalHierarchy

Synonym:

analytical hierarchy

Type of Math Object:

Definition

Major Section:

Reference

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