Pairs in P21: probability distributions which lead to estimates of the two‐phase structure seminvariants in the vicinity of 0 or π

The second sequence of nested neighborhoods of the two-phase structure seminvariant ϕ12 - ϕh1kl2 - ϕh1kl2 in the space group P21 is defined, and conditional probability distributions associated with the first four neighborhoods derived. In the favorable case that the variance of a distribution happens to be small, the distribution yields a particular reliable value for ϕ12. The most reliable estimates are obtained when ϕ12 ≃ ± π/2, thus facilitating enantiomorph specification in this space group.