Function abelianization 

pub fn abelianization(
    degree: usize,
    gens: &[Perm],
    cap: usize,
) -> Option<(u128, u128)>

The abelianisation G / [G, G] — the largest abelian quotient — as (order, exponent). The order is |G| / |[G, G]|; the exponent (lcm of coset orders) and whether it equals the order — i.e. whether Gᵃᵇ is cyclic — are the new structural content. None when |G| > cap.