The work is dedicated to the derivation of the 'functional' integral
representation of the disorder parameter. This derivation resolves the problem
of the choice of the so called modifed action as well as the problem of the
choice of the boundary conditions along the 'time' direction. The question of
the gauge fixing in the functional integral representation is also discussed.Comment: 8 pages. Revised version because of the minor LATEX error. Revised
version : additional references adde