Function cup 

pub fn cup(
    g: &FiniteGroup,
    modulus: usize,
    p: usize,
    q: usize,
    f: &[usize],
    h: &[usize],
) -> Vec<usize>

The cup product Cᵖ × Cᵠ → Cᵖ⁺ᵠ (Alexander–Whitney; Z/modulus coefficients, trivial action, no signs): (f ∪ h)(a₁,…,a_{p+q}) = f(a₁,…,a_p) · h(a_{p+1},…,a_{p+q}). It makes the obstruction groups a graded ring H*(G; A) — the multiplicative algebra binding all the k-invariant levels.