Decoding quotient-valued hiding answers #
The executable dual check only compares cosets of a row space. Decode each
reported register to the semantic canonical representative. This decoding is
used to return soundness to the existing finite game; it is not part of the
executable verifier and makes no computability claim about Fintype.equivFin.
The semantic dual map at a single reported stage.
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Selected registers are disjoint even for an unattainable reported output.
Decode all stage labels while preserving the original claimed output.
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Projection of the decoded answer extracts exactly its selected dual block.
On every already visited register the decoder only uses that same raw prefix.
Equal raw dual prefixes remain equal after decoding, even when the untested tails of the two claimed questions differ.
The prefix preceding the last stage determines the entire dual decoder.