  We propose that a Cooper pair in a high-$T_c$ superconductor might be in fact
a bound system $\rm eex\bar x$ of two electrons, a particle $\rm x$ and its
antiparticle. We assume $\rm eex\bar x$ is more massive than two free
electrons. We observe that $\rm eex\bar x$ should be stable in a solid if it is
in a low enough state in the solid. A solid which admits such a low state for
$\rm eex\bar x$ has some properties which seem closely related to the behavior
of HTS materials. The interaction of the $\rm x$-particle which binds the four
particles into $\rm eex\bar x$ has been discussed. We also discuss the scale of
the mass excess of $\rm eex\bar x$ relative to two free electrons. An
experiment designed to detect a bound system of two electrons with a mass
excess has been proposed.
