Jean-Marc Talbot The forall-exists<sup>2</sup> fragment of the first-order theory of atomic set constraints is Pi<sup>0</sup><sub>1</sub>-hard. 27-33 2000 74 Inf. Process. Lett. 1-2 db/journals/ipl/ipl74.html#Talbot00 http://dx.doi.org/10.1016/S0020-0190(00)00030-2