pub fn nilpotency_class(degree: usize, gens: &[Perm]) -> Option<usize>Expand description
The nilpotency class: the number of steps the lower central series γ₁ = G, γ_{k+1} = [G, γ_k]
takes to reach the trivial group, or None if it never does (G is not nilpotent). 0 is trivial,
1 abelian, 2 for D₄.