  A temporal (constraint) language is a relational structure with a first-order
definition in the rational numbers with the order. We study here the complexity
of the Quantified Constraint Satisfaction Problem (QCSP) for temporal
constraint languages.
  Our main contribution is a dichotomy for the restricted class of
dually-closed temporal languages. We prove that QCSP for such a language is
either solvable in polynomial time or it is hard for NP or coNP. Our result
generalizes a similar dichotomy of QCSPs for equality languages, which are
relational structures definable by Boolean combinations of equalities.
