Usually the electromagnetic field is naively thought as given by six independent
quantities E and B. However in chapter 2 the field was presented as
dependent on a four-component vector potential. In this chapter a different
approach is formulated, in which electromagnetic field is determined by
two scalar complex functions. This approach will serve as a starting point
for the following variational analysis given in the next chapter, where the
electromagnetic field is shown to depend only on a single complex function.
