Two space groups of a merge whose placements are within R_FREE_MARGIN (0.03) of each other in R-free
left the choice UNDECIDED. Where both placed the same number of copies they have the same parameters,
so the working reflections compare them as fairly as the free ones, and there are about twenty times as
many: the other group is now ruled out where the chosen placement's |F_obs - F_calc| is lower by 3
standard errors of the paired per-reflection difference over all reflections to the scoring limit.
Groups with different copy counts, and the tNCS carry rule, are unchanged.
Found on the timing benchmark's cytochrome C set started from the bovine AlphaFold model (the
sequence-exact one): three copies placed in both P 32 2 1 (R-free 0.427) and P 31 2 1 (0.437), so
MR_DECISION was UNDECIDED. Not a regression: the 2026-10-11 tNCS work ran this set with the horse
model, whose first copy did not place in P 31 2 1 at all, so P 32 2 1 was chosen with no tie (still
so at rc175 HEAD). With the 380 free reflections at 3 A the two hands differ by 0.010 +- 0.012 in
R-free; over all 7285 reflections by 0.029 at 11 standard errors. Now ENANTIOMORPH P 32 2 1, 3 copies,
placement CC 0.744.
MR replay survey of 193 sets (AlphaFold models): multi-copy UNDECIDED 7 -> 4, all three now correct
(7q6j P 21 21 21; both cytochrome C x06da sets P 32 2 1); one PAE-domain case (8tha) breaks its whole-
model hand tie towards the deposited group but stays UNDECIDED by the domain rule; no other set changes,
no wrong decision. Every tie the rule decided did so at 8.5-12.4 standard errors.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
leonarski_fandClaude Opus 5.5
6cdc063b4c