  The main motivation for this work was to find an explicit formula for a
"Szego-regularized" determinant of a zeroth order pseudodifferential operator
(PsDO) on a Zoll manifold. The idea of the Szego-regularization was suggested
by V. Guillemin and K. Okikiolu. They have computed the second term in a Szego
type expansion on a Zoll manifold of an arbitrary dimension. In the present
work we compute the third asymptotic term in any dimension. In the case of
dimension 2, our formula gives the above mentioned expression for the
Szego-redularized determinant of a zeroth order PsDO. The proof uses a new
combinatorial identity, which generalizes a formula due to G.A. Hunt and F.J.
Dyson. This identity is related to the distribution of the maximum of a random
walk with i.i.d. steps on the real line. The full version of this paper is also
available, math.FA/0212275.
