pub fn cycle_system(n: usize, p: u64) -> Vec<ModpEquation>Expand description
The canonical scalable mod-p obstruction: a cycle of differences xᵢ − x_{i+1} ≡ 1 (mod p) around
an n-cycle. Summing all n equations telescopes the left side to 0 and the right to n, so the
system is inconsistent exactly when n is not a multiple of p — the mod-p counting fact. For
even n with p > 2 ∤ n it is satisfiable over GF(2) yet refuted over GF(p): a family the parity
cut cannot see. (x − y is written x + (p−1)y.)