Complexity Results in Team Semantics: Nonemptiness Is Not So Complex
Pith reviewed 2026-05-25 08:14 UTC · model grok-4.3
The pith
Adding the nonemptiness atom to propositional logic yields NP-complete satisfiability and coNP-complete validity.
A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.
Core claim
The satisfiability problem for the extension of classical propositional logic with the nonemptiness atom NE is NP-complete, its validity problem is coNP-complete, and its model-checking problem is in P.
What carries the argument
The nonemptiness atom NE, which requires that every team of assignments is nonempty.
If this is right
- Satisfiability and validity remain in NP and coNP even though formulas are evaluated over teams rather than single assignments.
- Model checking can be performed by a deterministic polynomial-time procedure.
- Convexity and union closure suffice to keep the three problems from moving into higher complexity classes.
Where Pith is reading between the lines
- Similar complexity bounds may hold for other convex and union-closed extensions of propositional logic.
- One could test whether dropping union closure while retaining convexity changes the complexity of model checking.
Load-bearing premise
The extension of classical propositional logic with the nonemptiness atom is both convex and union closed.
What would settle it
A polynomial-time algorithm for satisfiability of formulas containing NE, or a reduction showing satisfiability is PSPACE-complete, would refute the stated complexity results.
read the original abstract
We initiate the study of the complexity-theoretic properties of convex logics in team semantics. We focus on the extension of classical propositional logic with the nonemptiness atom NE, a logic known to be both convex and union closed. We show that the satisfiability problem for this logic is NP-complete, that its validity problem is coNP-complete, and that its model-checking problem is in P.
Editorial analysis
A structured set of objections, weighed in public.
Referee Report
Summary. The manuscript initiates the study of complexity-theoretic properties of convex logics in team semantics. It focuses on the extension of classical propositional logic with the nonemptiness atom NE (CPL+NE), a logic known to be both convex and union closed. The central claims are that the satisfiability problem is NP-complete, the validity problem is coNP-complete, and the model-checking problem is in P.
Significance. If the results hold, they establish baseline complexity classifications for convex logics under team semantics and demonstrate that adding the NE atom does not increase complexity beyond that of classical propositional logic. The adaptation of standard propositional reductions while leveraging the known convexity and union-closure properties provides a clean foundation for future work on other convex team-based logics.
minor comments (2)
- [Abstract] The abstract states the three complexity results without indicating the proof techniques or reduction strategies employed; adding one sentence on the high-level approach would improve accessibility.
- The manuscript would benefit from an explicit statement of the team-semantics definitions for the connectives and the NE atom early in the paper to make the reductions self-contained.
Simulated Author's Rebuttal
We thank the referee for their positive recommendation to accept the manuscript and for the accurate summary of our results on the complexity of CPL+NE under team semantics.
Circularity Check
No circularity in standard complexity classifications
full rationale
The paper establishes NP-completeness of satisfiability, coNP-completeness of validity, and P membership of model-checking for CPL+NE by adapting standard propositional reductions to team semantics. Convexity and union closure are invoked as known external properties of the logic rather than derived internally. No equations, fitted parameters, self-definitional steps, or load-bearing self-citations appear in the derivation chain; the results rest on independent reductions and do not reduce to their own inputs by construction.
Axiom & Free-Parameter Ledger
axioms (2)
- standard math Classical propositional logic axioms and semantics
- domain assumption Team semantics definition and convexity/union-closure of NE
Reference graph
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