  The relation between two approaches to the su(2)-algebraic many-fermion model
is discussed: (1) the BCS-Bogoliubov approach in terms of the use of the
quasiparticles representing all the degrees of freedom except those related to
the Cooper-pairs and (2) the conventional algebraic approach in terms of the
use of the minimum weight states, from which the Cooper-pairs are excluded. In
order to arrive at the goal, the idea of the quasiparticles is brought up in
the conservation of the fermion number. Under the c-number replacement for the
three su(2)-generators, the quasiparticles suggested in this paper are reduced
to those in the BCS-Bogoliubov approach. It is also shown that the two
approaches are equivalent through the c-number replacement. Further, a certain
modification of the BCS-Bogoliubov approach is discussed.
