According to 78), S = L + fF, and it follows that
lor S = lor L + lor fF.
The symbol ‘lor’ denotes a differential process which in lor fF, operates on the one hand upon the components of f, on the other hand also upon the components of F. Accordingly lor fF can be expressed as the sum of two parts. The first part is the product of the matrices (lor f) F, lor f being regarded as a 1 × 4 series matrix. The second part is that part of lor fF, in which the diffentiations operate upon the components of F alone. From 78) we obtain
fF = -F*f* - 2L;
hence the second part of lor fF = -(lor F*)f* + the part of -2 lor L, in which the differentiations operate upon the components of F alone. We thus obtain
lor S = (lor f)F - (lor F*)f* + N,
where N is the vector with the components
Nh = ½(∂f₂₃/∂xh F₂₃ + ∂f₃₁/∂xh F₃₁ + ∂f₁₂/∂xh F₁₂ + ∂f₁₄/∂xh F₁₄
+ ∂f₂₄/∂xh F₂₄ + ∂f₃₄/∂xh F₃₄
- ∂F₂₃/∂xh f₂₃ - ∂F₃₁/∂xh f₃₁ - ∂F₁₂/∂xh f₁₂ - ∂F₁₄/∂xh f₁₄