  A general theory of superconductivity based on the pairing of electrons that
belong to different electronic bands is presented. These electronic bands arise
because of a symmetry breaking at the critical temperature in such a way that
one electron sees the other as if its mass would be negative. This symmetry
breaking leads also to an energy gap (centered round of the Fermi level)
between the coupled electrons. Under the assumption that electric resistance is
due to electron-phonon interaction, a general equation from which the
fundamental properties of any metallic superconductor can be derived is also
presented. In the frame of this theory, the electron-phonon interaction (or
electric resistance) is cancelled out by the electron-electron interaction in
the super-conducting state. Moreover, the Bardeen-Cooper- Schrieffer (BCS)
theory is a particular case of our theory and equations, a matter, which leads
to a better overall agreement with experimental data.
