  We consider quantum mechanical Yang-Mills theories with eight supercharges
and a $Spin(5) \times SU(2)_R$ flavor symmetry. We show that all normalizable
ground states in these gauge theories are invariant under this flavor symmetry.
This includes, as a special case, all bound states of D0-branes and D4-branes.
As a consequence, all bound states of D0-branes are invariant under the
$Spin(9)$ flavor symmetry. When combined with index results, this implies that
the bound state of two D0-branes is unique.
