pub fn php_symmetries(n: usize) -> Vec<CubeSym>Expand description
The generating symmetries of the pigeonhole cover: adjacent transpositions of pigeons (rows) and
of holes (columns). Together they generate the full grid symmetry group Sₙ × Sₙ₋₁ — pure
coordinate permutations (no phase flips). Each is a CubeSym over the n*(n-1) grid variables.