s2::cellid
pub const POS_TO_IJ: [[u8; 4]; 4] = [[0, 1, 3, 2], [0, 2, 3, 1], [3, 2, 0, 1], [3, 1, 0, 2]]
=
[[0, 1, 3, 2], [0, 2, 3, 1], [3, 2, 0, 1], [3, 1, 0, 2]]