  The impossibility of ascribing definite states to the constituents of an
entangled system restricts the scope of Pauli's principle in this context. We
analyze the conceptual and physical aspects of the problem by studying the
actual scope of the principle and the possibility of extending the concept of
exclusion in correlated systems. When the entanglement is weak, as in the
archetypical case of the Helium atom, the principle can be applied in an
approximated way. The concept of non-complete set of properties plays a crucial
role in the argument, which also clarifies the physical meaning of the atomic
quantum numbers; they are a multi-particle property, not an one-electron one.
In contrast, for strong entanglement the excluded states are independent of the
principle. We describe some of these states, many times determined by
symmetries of the multi-fermion state.
