  Models with competing interactions, for example the ANNNI model, can have
special points at which the ground state is infinitely degenerate, so-called
multiphase points. Small perturbations can lift this degeneracy and give rise
to infinite sequences of long-period phases. This paper compares the effect of
three possible perturbations, quantum fluctuations, thermal fluctuations and
the softening of the spins from their quantised positions.
