A. Yu. Baryshnikov, A. B. Livchak, “The languages ${\rm PQL}$ and ${\rm FO}+{\rm LFP}$ are equivalent even without the presence of order”, Izv. Vyssh. Uchebn. Zaved. Mat., 1996, no. 4, 18–23; Russian Math. (Iz. VUZ), 40:4 (1996), 16–21
A. B. Livchak, “Formula subsets of the ordered group of integers”, Izv. Vyssh. Uchebn. Zaved. Mat., 1977, no. 8, 105–107; Soviet Math. (Iz. VUZ), 21:8 (1977), 81–83
Contact us: