abstract. We establish that the quantifier alternation hierarchy of formulae of Second-Order Propositional Modal Logic (SOPML) induces an infinite corresponding semantic hierarchy ...
In 1974 R. Fagin proved that properties of structures which are in NP are exactly the same as those expressible by existential second order sentences, that is sentences of the form...
Attempts at classifying computational problems as polynomial time solvable, NP-complete, or belonging to a higher level in the polynomial hierarchy, face the difficulty of undecid...