Function explains_divergence 

pub fn explains_divergence(
    complete_comparison: bool,
    open_positions: [Option<usize>; 2],
    first_divergent_positions: Option<(Option<usize>, Option<usize>)>,
) -> bool

Whether a pattern difference explains a divergence: the comparison was one strict enough for bitwise parity (complete_comparison), and the open that found the difference (placed by open_position in each run’s log) is recorded before the first divergent record in both logs (first_divergent_positions, the comparator’s positions of that record), so the two runs had done the same things up to that open. Without every position nothing is attributed.