Conjecture on properness and incomparability of positive free logic systems

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The paper considers the classical positive free logic systems appearing in Theorem

, namely the systems ordered there by inclusion, together with $\mathbf{CPF}^{\begin{sideways}\begin{sideways}$\iota$\end{sideways}\end{sideways} H}$, $\mathbf{CPF}^{\begin{sideways}\begin{sideways}$\iota$\end{sideways}\end{sideways} S}$, and $\mathbf{FD2}$. **Conjecture on system inclusions.** (a) All inclusions of Theorem

are proper. (b) \mathbf{CPF}^{\begin{sideways}\begin{sideways}\iota\end{sideways}\end{sideways} H} and \mathbf{CPF}^{\begin{sideways}\begin{sideways}\iota\end{sideways}\end{sideways} S} are incomparable. (c) \mathbf{CPF}^{\begin{sideways}\begin{sideways}\iota\end{sideways}\end{sideways} H} and FD2\mathbf{FD2} are incomparable. This conjecture concerns the exact relationships among the positive free logic systems; the supplied text gives no evidence that these properness and incomparability claims have been resolved.

References

Primary source

Nils Kürbis, “Normalisation for Positive Free Logics without and with Definite Descriptions”, arXiv:2606.11735 (2026).

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