Function schreier_sims 

pub fn schreier_sims(degree: usize, generators: &[Perm]) -> Bsgs

Schreier–Sims. Build a BSGS for the permutation group on degree points generated by generators (each a permutation of {0,…,degree−1}). Deterministic incremental construction: seed the chain with the generators, then repeatedly sift every Schreier generator (u·s divided by its transversal element, Schreier’s lemma) into the chain, adding any non-trivial residue as a new strong generator (extending the base as needed), until every Schreier generator sifts to the identity — the completeness condition.