Before revision:  We apply the powerful theory of characteristic functions and Hilbert transforms , which have not been used in this combination before .
After revision:  We apply the powerful theory of characteristic functions and Hilbert transforms . The latter concept is used to express the characteristic function (c.f.) of the random variable (r.v.) \max(Y, 0) in terms of the c.f. of the r.v. Y. The present paper applies this concept for the first time in mathematical finance .