Differentiable perturbation of unbounded operators

Abstract

If $A(t)$ is a C^{1,\al}-curve of unbounded self-adjoint operators with compact resolvents and common domain of definition, then the eigenvalues can be parameterized $C^1$ in $t$. If $A$ is $C^\infty$ then the eigenvalues can be parameterized twice differentiable.Comment: amstex 9 pages. Some misprints correcte