Undecidable
Not decidable as a result of being neither formally provable nor unprovable.
See also
Gödel's First Incompleteness Theorem, Gödel's Second Incompleteness Theorem, Recursively Undecidable, Rice's Theorem, Richardson's TheoremExplore with Wolfram|Alpha
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Cite this as:
Weisstein, Eric W. "Undecidable." From MathWorld--A Wolfram Resource. https://mathworld.wolfram.com/Undecidable.html