  Following the deformed boson scheme leading to the su(1,1)-algebra, a certain
simple boson system is deformed in the framework of the second
Holstein-Primakoff representation. With the aid of the MYT boson mapping, the
second representation arrives at the first Holstein-Primakoff representation.
The su(1,1)-algebraic model obtained in this procedure is compared with that in
the Schwinger representation investigated by three of the present authors
(A.K., Y.T. and M.Y.).
