  A formulation of Covariant Canonical Quantization is discussed, which works
on an extended Hilbert space and reduces to conventional canonical quantization
when constraining to the solution of the field equation a priori. From the
formal point of view it may be seen as a formalism between the canonical
operator and the functional integral approach. A covariant number operator and
two symmetric vacua are constructed. By that means, certain well-known
quantities like the LSZ formula are rederived via a projection limit. The
time-ordering operator can be replaced by taking into account the mirrored
vacuum as well. Then the quantum field theoretical divergences like the vacuum
energy arise a posteriori when a spacetime split is performed. The role of the
vacuum energy in different contexts is then discussed in general.
