sentences:  But the definition from the previous subsection immediately implies that any vector of zero scalar square is orthogonal to itself.Hence, the isotropic line generated by a null vector ν is a subset of its orthogonal complement .The formal definition of the orthogonal complement of a vector subspace in a pseudo-Euclidean space gives a perfectly well-defined result, which satisfies the equality due to the quadratic form's non-degeneracy.