  Systems of up to twelve electrons and six holes on the Haldane sphere are
studied by exact numerical diagonalization. The low lying states of the system
involve bound excitonic complexes such as (X^n)-. The angular momenta of these
complexes and the pseudopotentials describing their interaction are determined.
The similarity to the electron pseudopotential suggests the possibility of
incompressible ground states of a gas of X- ions for nu<=1/3. The nu=1/3 state
of three X-'s is found.
