  It is proposed to make formulation of second quantizing a bosonic theory by
generalizing the method of filling the Dirac negative energy sea for fermions.
We interpret that the correct vacuum for the bosonic theory is obtained by
adding minus one boson to each single particle negative energy states while the
positive energy states are empty. The boson states are divided into two sectors
; the usual positive sector with positive and zero numbers of bosons and the
negative sector with negative numbers of bosons. Once it comes into the
negative sector it cannot return to the usual positive sector by ordinary
interaction due to a barrier. It is suggested to use as a playround models in
which the filling of empty fermion Dirac sea and the removal of boson from the
negative energy states are not yet performed. We put forward such a naive
vacuum world and propose a CPT-like theorem for it.We study it in detail and
give a proof for $\lambda/4 (\phi^+\phi)^2$ theory. The CPT-like theorem is a
strong reflection, but does not include inversion of operator order which is
involved in the ordinary CPT theorem. Instead it needs certain analytic
continuation of the multiple wave function when the state is formulated as a
finite number of particles present.
