A screw axis extinguishes a row; a glide plane extinguishes a zone. The search scored the
first and had no candidate that could carry the second, so a small molecule whose cell and
whose rotations were both found correctly stopped one glide short of its group.
The zone is keyed by the rotation part of the improper operator, so a glide and its centring
partner - the c and the n of the same plane - are one zone rather than two scored twice. A
Sohncke group has no improper operator at all, so on chiral data the zone loop never runs and
every Sohncke candidate scores what it scored before, bit for bit. That is why this is offered
inline rather than behind a flag; it was still measured, on 140 protein datasets, and no
protein answer moves and no non-Sohncke candidate reaches the top of the ranking.
A glide is judged per reflection rather than on the zone's sum. The statistic is linear in the
number of absences at fixed deadness, and a plane holds hundreds to thousands of reflections
where a row holds tens, so a sum reaches hundreds of nats on a class that is merely a few
times weak; per reflection the false and the genuine zones separate by a factor of nine. An
unmeasurable zone refuses its candidate rather than abstaining, because a glide is an extra
claim on top of a group that already fits without it.
Both readings are reported on every run. A crystal of chiral molecules cannot have a glide, so
a reader who knows the sample is a protein must be able to see the Sohncke group without
processing the images again.
A centre of symmetry is not offered at all: a candidate is enumerated only when its absences
differ from a Sohncke candidate's, and an inversion centre predicts exactly what its Sohncke
subgroup predicts. It cannot be claimed from intensities and this does not claim it.
Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01EFEJG6WBQv8th4UJFNe53N
leonarski_fandClaude Opus 5
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