Oracle

An oracle is a black box that can give an answer to any instance of a certain problem in a single operation. The problem ⁠can be of any complexity class, or it can even be an undecidable problem such as the halting problem.

• 0': decide the halting problem for computable programs.
• 1': decide the halting problem for programs containing 0'
• Ω': decide the halting problem of any program, including programs containing Ω'^{[citation needed]}
• Ω2': decide if a programs is well-founded (do not create any kind of paradox)^{[citation needed]}

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