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Geyer, Hahne, and Scholtz Reply:The interacting-boson model (IBM) is a model of interacting bosons which serves as a framework to study collective nuclear spectra with algebraic techniques. ^ It appears in several different guises. Simplicity is one input requirement and therefore the Hamiltonian is parametrized in terms of sums of scalar operators which are at most quadratic in the generators of the group under consideration, which initially was SU(6).Two further aspects normally characterize the IBM. From its inception the model accommodated microscopic input by assuming the fermion valence number N to characterize the relevant SU(6) representations, while it was also understood that the IBM parameters depended on TV and could themselves therefore be parametrized, among other possibilities, in terms of TV. The second aspect, often not explicitly stated, is that one still has to choose a form for the transition operators to be used within the IBM context. The simplest choice of a linear combination of the appropriate generators is usually made.Against this background the exposition in our Letter^ should be evaluated and compared with the remarks of the preceding Comment. ^ We reiterate that the SO(7) dynamical symmetry can be identified within the IBM framework described above. In particular there is nothing fundamentally "more" fermionic about this symmetry than any of the traditional IBM symmetries. Furthermore the conclusion^ that our analysis "implies a conflict" between an SO (7) description of the Pd-Ru nuclei and the analysis by Stachel, van Isacker, and Heyde"^ is incorrect. What is stated and im-plied^ is that a situation previously described in terms of a transition between two IBM dynamical symmetries can, within the IBM, also be interpreted in terms of another single dynamical symmetry.The IBM quadrupole operator adopted by us^ is viewed in the preceding Comment^ as distracting from the "simplicity of the IBM." Being a single generator, the choice could hardly be any simpler. Furthermore the often expressed suspicion that non-Hermiticity per se is undesirable is unfounded. (Non-Hermitean operators are really not so uncommon. For instance, they have appeared in the microscopic derivation of the shell model many years ago.) What is required of an operator representing physical variables is that it produces, as in our case, real values for the associated measurements. It should be noted, furthermore, that in contrast to the fermion case, simple, orthogonal basis states can be used in the boson model. In general, the boson eigenfunctions have correlations with respect to this basis and, as already noted,'^ turn out to be the U(5) states in the case of the SO (7) Hamiltonian of Eq. (10) of Ref. 2.Finally, the fermion-dynamic-symmetry model^ indeed deserves further study. This model offers, in terms of normal-parity shell-model states, a very specific inter-pretation^ of the microscopically linked parameters TV and n, which does seem to be supported by the analysis^ of the Pd-Ru data. Further tests of this...

It is shown that it is not necessary to resort to an explicit mapping of the fermion basis into the boson space when bifermion excitations are treated in a boson picture. One may use the usual ideal boson basis in the boson space, Under certain circumstances this may lead to the occurrence of spurious states. However, these do not mix with the physical states and they can be identified by means of a simple procedure which is developed within the framework of the Dyson boson method. The results are illustrated by means of three interesting cases in the Sp(4) model.