  As a first step to derive the IBM from a microscopic nuclear hamiltonian, we
bosonize the pairing hamiltonian in the framework of the path integral
formalism respecting both the particle number conservation and the Pauli
principle. Special attention is payed to the role of the Goldstone bosons. We
construct the saddle point expansion which reproduces the sector of the
spectrum associated to the addition or removal of nucleon pairs.
