  N=2 supersymmetric Yang-Mills theories for all classical gauge groups, that
is, for SU(N), SO(N), and Sp(N) is considered. The equations which define the
Seiberg-Witten curve are proposed. In some cases they are solved. It is shown
that for (almost) all models allowed by the asymptotic freedom the 1-instanton
corrections which follows from these equations agree with the direct
computations and with known results.
