// the first is in the a1-d1-d4 triangle. If the first king is on the a1-d4
// diagonal, the other one shall not to be above the a1-h8 diagonal.
std::vector<std::pair<int, Square>> bothOnDiagonal;
// the first is in the a1-d1-d4 triangle. If the first king is on the a1-d4
// diagonal, the other one shall not to be above the a1-h8 diagonal.
std::vector<std::pair<int, Square>> bothOnDiagonal;