  The program TOPAZ0 was developed for computing a variety of physical
observables which are related to the e+e- annihilation into fermion pairs and
to the large angle Bhabha scattering around the Z resonance. Among them, the Z
parameters or pseudo-observables, the de-convoluted cross sections and those
dressed with QED radiation, and finally the forward-backward asymmetries. The
calculations are performed both for a completely inclusive experimental set-up
and for a realistic one, i.e. a set-up with cuts on the acollinearity angle, on
the energy of the outgoing fermions or on their invariant mass and angular
acceptance. The new version, 4.0, includes several innovative features. First
of all, the most important new capabilities since previous versions are
recently computed electroweak and QCD correction factors that are relevant at
the Z resonance in the light of the present experimental accuracy. Among them,
the effect of the next-to-leading O(alpha^2 m_t^2) corrections and those
radiative corrections to the hadronic decay of the Z which provide complete
corrections of O(alpha alpha_s) to Gamma(Z --> q\bar{q}) with q=u,d,s,c and b.
Secondly, the program has been upgraded to cover two-fermion final states at
LEP 2 energies, where some of the assumptions made for earlier versions are no
longer valid. In particular, to this aim all the electroweak radiative
corrections that are negligible at the Z peak, but relevant far from it, have
been added for s-channel processes, e.g. purely weak boxes, next-to-leading
O(alpha^2) and leading O(alpha^3) QED corrections.
