Function abductive_explanation 

pub fn abductive_explanation(
    rules: &[NQuin],
    observation: u64,
    explains: u64,
) -> Option<u64>

Abductive inference — walk BACKWARD along explanatory edges (hypothesis →explains→ effect, predicate == explains) from an observed effect to the root hypothesis that accounts for it. Returns that root, or None if the observation has no explanation in the rule set. Zero-heap.