  Sato introduced the tau-function to describe solutions to a wide class of
completely integrable differential equations. Later Segal-Wilson represented it
in terms of the relevant integral operators on Hardy space of the unit disc.
This paper gives another representation of the tau-functions by the Weyl
functions for 1d Schr\"odinger operators with real valued potentials, which
will make it possible to extend the class of initial data for the KdV equation
to more general one.
