/// Near-equality comparison
friend bool Close(const Quaternion& q1, const Quaternion& q2, T eps)
{
for(std::size_t i=0; i!=4; ++i)
{
T u = q1.At(i);
T v = q2.At(i);
T d = std::abs(u-v);
bool ca = d <= std::abs(u)*eps;
bool cb = d <= std::abs(v)*eps;
if(!ca && !cb) return false;
}
return true;
}
