On the Eigenvalue Problem of the su(1,1)-Algebra and the Coupling Scheme   of Two su(1,1)-Spins
  After recapitulating the eigenvalue problem of the su(1,1)-algebra in the conventional form, the same problem is treated in an unconventional form, in which the eigenvalue is pure imaginary. Further, the coupling scheme of two su(1,1)-spins is discussed in the framework of two possibilities, in which certain new aspects appear. Finally, the coupling scheme developed in this paper is applied to a concrete example, which will serve boson realization of the so(4)- and the so(3,1)-algebra presented in the next paper. 
S.Nishiyama (Kochi Univ., Japan), C.Providencia (Univ. de Coimbra,   Portugal), J da Providencia (Univ. de Coimbra, Portugal...