Eigenvalues in gaps of selfadjoint operators in Pontryagin spaces
arXiv:1111.3011
Abstract
Given an open real interval Δ and two selfadjoint operators A_1, A_2 in a Π_κ-space with n-dimensional resolvent difference we show that the difference of the total multiplicities of the eigenvalues of A_1 and A_2 in Δ is at most n+2κ.