pub fn bockstein(g: &FiniteGroup, n: usize, c: &[usize]) -> Vec<usize>Expand description
The Bockstein β : Hⁿ(−; Z/2) → Hⁿ⁺¹(−; Z/2) — the connecting homomorphism of the short exact
sequence 0 → Z/2 →(×2) Z/4 → Z/2 → 0. By a theorem of Steenrod, β = Sq¹. Computed honestly: lift
the Z/2-cochain to Z/4, take δ over Z/4 (which is even on a Z/2-cocycle), divide by 2, and
reduce mod 2. The lowest genuine Steenrod square, reached as a connecting map rather than a cup-square.