  We study the properties of a quantum impurity embedded in a superconducting
host. The superconductor is described by the negative U Hubbard model while the
impurity introduces a repulsive interaction to the system. We discuss the
influence of this `on-impurity' Coulomb repulsion on the local properties
(density of states, electron pairing) of the superconductor. We show the
condition of pi - like behaviour, defined as two subsystems having a phase
difference of pi, in the system by using a proper combination of attractive
pairing interaction and repulsive one located at impurity site.
