PSPACE membership for the validity problem of RmbC

Prove or refute the conjecture that the validity problem for RmbC belongs to PSPACE.

Background

The paper proves that validity for RmbC is coNP-hard and belongs to coNEXPTIME, hence to 2-EXPTIME. The resulting gap leaves open whether a substantially lower upper bound is possible. The authors specifically conjecture PSPACE membership but do not provide a proof.

References

We conjecture, without proof, that \mathrm{Val}(\mathrm{RmbC}) may be in \textsf{PSPACE}.

— Self-extensional logics of formal inconsistency: Decidability and limits for paraconsistency  (2608.28443 - Coniglio et al., 28 Aug 2026) in Speculative Remark in Section 6.2, “An upper bound”