UNITARY OPERATORS ON SPACE π

In the Pontrjagin space π, there is a basic result that for any unitary (or self adjoint) operator, there exists a non-positive K-dimensional invariant subspace. For a self adjoint operator A on Krien space π, if π=H⊕is a regular decomposition of π, and PAPis a compact operator, then there exists a maximum non-positive in-