  Assuming that the phase transition between the Wigner solid and the Laughlin
liquid is first-order, we compare ground-state energies to find features of the
phase diagram at fixed $\nu$. Rather than use the Coulomb interaction, we
calculate the effective interaction in a square quantum well, and fit the
results to a model interaction with length parameter $\lambda$ roughly
proportional to the width of the well. We find a transition to the Wigner solid
phase at high density in very wide wells, driven by the softening of the
interaction at short distances, as well as the more well-known transition to
the Wigner solid at low density, driven by Landau-level mixing.
