6iu9 (deposited P3_1, merohedrally twinned at 0.4 or more by its 321 law: H 0.097, CC 0.79) went
from P3_1 to P3_121 when the penalised per-frame scale smoother (495f6a97b) landed; the ingest
partiality fix alone (7d6c201e9) keeps P3_1. Bisected on the two binaries: smoother-only 6iu9 P3_121,
partiality-only P3_1. The smoother only removed the luck: the P3_1 answer rested on the
Lorentz-filtered arm's added-operator R contrast reading 0.71 against a bound of 0.72 (the
all-observation arm already passed 32 at 0.82); better scaling moved it to 0.87, no gate refused, and
the twin-immune zone - which reads -401 nats, acentric - is only consulted where a gate fired.
A near-perfect twin passes every agreement gate by construction (H ratio 0.97 here); only the zone
can refuse it. It was confined to refusals because a genuine trigonal crystal read -46 nats with no
gate firing; on the battery 5uth (genuine P3_121, twinned by a 622 law, other-law CC 0.14) reads
-206. The reason: the centric density was untwinned, but a twin by a law OTHER than the zone's
operators reaches the zone as it reaches every reflection, so a genuine zone reads 0.81 at a = 0.2.
The operators' own twin law cannot reach their zone, so only the centric side needs it.
- TwinningAnalysis: the zone's centric density is the twinned one at a caller-given fraction
(weighted sum of two chi^2_1, via exp(-y) I0(y)); the control's calibration expectation is taken
at the same fraction (-KL(acentric || centric_a), -0.130 at a = 0 as before). At a = 0 nothing
changes.
- SearchSpaceGroup: twin_fraction_outside = the fraction implied by the strongest CC of a lattice
rotation outside the group, relative to the group's own mean CC, through rho = 2a(1-a)/((1-a)^2+a^2);
exported for the adopted group and used by Rugnux's TwinZoneVerdict and the zone report.
- New Stage A test: a candidate that does not hold every lattice rotation, on a P1 merge whose <|L|>
is in the partial-twin band [0.375, 0.44), is refused when the zone over one of its index-2
subgroups reads acentric by 20 nats (the TwinZoneVerdict bound), unless zones_ambiguous. The band's
lower end is the L-test gate's: below it something else compresses the zones too (a pseudo-cubic
small-molecule set, cuhf2, read its 422 zone at 0.64 beside a control at 0.58 and was turned to
P222 without it).
Zone evidence (calibrated, at the other-law fraction): 6iu9 32 -230 / -143 (refused, P3_1);
5uth +209 / +33 (P3_121 kept); 8xtg +324 / +65; 6vww P6 +20 / +8.5; 7k1l P6 +8 / +7.5.
Battery (open+inhouse, targeted, against 20261004-2350 all2-full; only beyond-noise change listed):
- 6iu9: fail -> pass, P3_121 -> P3_1, R_meas 17.4% -> 14.4%, ISa 4.6 -> 5.4, R-free 0.318 -> 0.327.
- unchanged: 6iu5, 6iu6, 6iu8 (P3_1), 5uth, 5j23, insu_H_x06da_twin/notwin, 6vww, 7k1l, 8xte, 8xtg,
9i80, 4bwl, 2wnq, 8c3e, 2wnn, 2xfw, 5ebi, 6p8j, 6z9g, 6rlr, 6toc, 3mc4; 321/312 controls 5lzl,
6w4h, 9gqg, 6pxb, 9z72; all 14 small-molecule sets (cuhf2 checked again after the band).
- private subset (8 sets): no change beyond noise.
Tests: [twinning] (new: zones read at the other twin laws' fraction), SearchSpaceGroup*.
Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01K5K8jvPPbmCrbqnWkddTuB
leonarski_fandClaude Opus 5.5
f9ffc3d837
