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A term in software programming used to describe a coding problem (or "bug") that seems to defy testing by presenting itself exclusively in published, released or demonstrated code, but not at any point during debugging. It disappears or alters its characteristics when an attempt is made to study it. The bug both exists and doesn't exist and simultaneous points in time -- the reference is to Heisenberg's Uncertainty Principle (or to be direct, the quantum cat in the Heisenberg scenario).
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