pub fn e_real(signature: i128, n: usize) -> Option<u128>Expand description
The real cohomological invariant eₙ of a form of signature σ over ℝ
(the surreal backend’s leg). Over ℝ, W(ℝ) ≅ ℤ via the signature and
Iⁿ = 2ⁿℤ, so the form is in Iⁿ iff 2ⁿ | σ, and then
eₙ = (σ / 2ⁿ) mod 2 — the staircase reads the 2-adic expansion of the
signature. Returns None when the form is not in Iⁿ (so eₙ is undefined).
This is the infinite tower the finite-field and Q_p legs truncate.