Pairs in P2₁: probability distributions which lead to estimates of the two-phase structure seminvariants in the vicinity of ±π/2

The second sequence of nested neighborhoods of the two-phase structure seminvariant φ₁₂ - φ_h1kl2 - φ_h1kl2 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.