  The possible neutron-antineutron oscillation is described by an effective
quadratic Lagrangian analogous to the BCS theory. It is shown that the
conventional equal-time anti-commutation relations of the neutron variable
$n(t,\vec{x})$ are modified by the baryon number violating terms. This is
established by the Bjorken--Johnson--Low prescription and also by the canonical
quantization combined with equations of motion. This novel canonical behavior
can give rise to an important physical effect, which is illustrated by
analyzing the Lagrangian that violates the baryon number but gives rise to the
degenerate effective Majorana fermions and thus no neutron-antineutron
oscillation. Technically, this model is neatly treated using a relativistic
analogue of the Bogoliubov transformation.
