in mp_utils.hpp, unitary_det_4x4()
if (_pivot % 2 == +0)
{
expansion_sub(_det2p, _det1p, _sum_1);
expansion_sub(_det4p, _det3p, _sum_2);
}
else
{
expansion_sub(_det2p, _det1p, _sum_1);
expansion_sub(_det4p, _det3p, _sum_2);
}
both conditions are the same