By definition, an indefinite inner product space is a real or complex vector space together with a symmetric (in the complex case: hermi- tian) bilinear form prescribed on it so that the corresponding quadratic form assumes both positive and negative values. The most important special case arises when a Hilbert space is considered as an orthogonal direct sum of two subspaces, one equipped with the original inner prod- uct, and the other with -1 times the original inner product. The subject first appeared thirty years ago in a paper of Dirac [1] on quantum field theory (d. also Pauli [lJ)....
By definition, an indefinite inner product space is a real or complex vector space together with a symmetric (in the complex case: hermi- tian) biline...
