= Py φz y* + Pz* φl y + Pl φ*y z.
= Py φx y + Pz φx z + Pl φx l,
which coincides with (Pφx) according to our definition.
Examples of this type of vectors will be found on page 36, Φ = wF, the electrical-rest-force, and ψ = 2wf*, the magnetic-rest-force. The rest-ray Ω = iw[Φψ]* also belong to the same type (page 39). It is easy to show that
Ω = -i | w₁ w₂ w₃ w₄ |
| Φ₁ Φ₂ Φ₃ Φ₄ |
| ψ₁ ψ₂ ψ₃ ψ₄ |
When (Ω₁, Ω₂, Ω₃) = 0, w₄ = i, Ω reduces to the three-dimensional vector
| Ω₁, Ω₂, Ω₃ | = | Φ₁ Φ₂ Φ₃ |
| |