Near-perfect twins of a subgroup are undecidable from intensities, and a merge
in the higher group cannot be twin-refined. Where the adopted group may have
absorbed a twin law - a twin gate refused it and was overruled, or a group above
P1 was adopted on a merge that read twin-like before the search - the same
observations are also merged in a subgroup and written beside the answer, with
the twin law and its fraction in _pdbx_reflns_twin.
The subgroup is the one a decision named (the group a refused promotion was
adopted over, the indexed lattice's group a metric re-ask promoted from), else
the index-2 subgroup the search confirmed as a finalist whose lost two-fold
agrees worst with the intensities. It is merged from the same engine, to the
answer's resolution, without writing per-frame scales back; it carries the
answer's free set (flags read off the answer's merge by the adopted group's
asymmetric unit) and is written in the subgroup's reference and standard
setting (a C 1 1 2_1 description is reduced to P 1 2_1 1). The fraction is
Yeates' H on the pairs the law relates (1/2 - median H, a lower bound).
At most one file; other qualifying subgroups are named in the report
(TWIN_SUBGROUP_* keys). The answer's files are byte-identical.
IndexTwoTwinSubgroups and EstimateTwinLawFraction are new and tested; the
point-group ledger now carries each hypothesis's representative group.
Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01SVmAWnzCmRKAXVUCdc4iNi
leonarski_fandClaude Opus 5.5
475df9e5cb