An addendum to Krein's formula

We provide additional results in connection with Krein's formula, which describes the resolvent difference of two self-adjoint extensions A(1) and A(2) of a densely defined closed symmetric linear operator k with deficiency indices (n, n), n is an element of boolean OR{infinity}. In particular, we explicitly derive the linear fractional transformation relating the operator-valued Weyl-Titchmarsh M-functions M-1(z) and M-2(z) corresponding to A(1) and A(2). (C) 1998 Academic Press.