  It is decidable if a set of numbers, whose representation in a base b is a
regular language, is ultimately periodic. This was established by Honkala in
1986.
  We give here a structural description of minimal automata that accept an
ultimately periodic set of numbers. We then show that it can verified in linear
time if a given minimal automaton meets this description.
  This thus yields a O(n log(n)) procedure for deciding whether a general
deterministic automaton accepts an ultimately periodic set of numbers.
