,
Guo-Qiang Zhang
Creative Commons Attribution 4.0 International license
We study the discrete point-based fragment of Ensemble Logic EL(ℕ) over the natural numbers, a logic combining displacement φ_u, term-dependent metric modalities ☐_t and ♢_t with respect to an additive term t, Boolean connectives, and first-order quantification over ℕ. Motivated by the need for a unified symbolic representation of biomedical knowledge with temporal, spatial, and multimodal metric content, we develop the foundational discrete theory of the formalism. We give syntax and semantics, and prove a forward embedding of EL(ℕ) (over a finite proposition set 𝒫) into first-order monadic Presburger arithmetic FO(ℕ,<,+;𝒫). This embedding yields the analytical upper bounds, while a reduction from nondeterministic two-counter Turing machines with recurring control states proves that satisfiability is Σ¹₁-complete and validity is dually Π¹₁-complete. Expressively, EL(ℕ) strictly extends the star-free ω-languages and is incomparable with the ω-regular languages: it defines the non-ω-regular counting language {a^m b^m c^m d^m∣ m ≥ 1}⋅Σ^ω, whereas a delimited parity language remains outside the logic by a quantifier-bounding argument combined with classical circuit lower bounds for parity. On the proof-theoretic side, we present a sound Hilbert system ℋ_EL and establish completeness relative to monadic Presburger validity as oracle, noting that completeness relative to plain Presburger arithmetic is impossible. We also prove that the existential fragment ∃EL(ℕ) has NP-complete satisfiability and coNP-complete unsatisfiability. Finally, we show that finite active-domain model-checking has PTIME data complexity and PSPACE-complete combined complexity. Together, these results give a precise decidability, expressiveness, proof-theoretic, and model-checking baseline for subsequent algorithmic applications of Ensemble Logic in biomedicine. This work is a part of the Symbolic Biomedicine program championed by the corresponding author.
@InProceedings{droste_et_al:OASIcs.TIME.2026.4,
author = {Droste, Manfred and Zhang, Guo-Qiang},
title = {{Discrete Linear Ensemble Logic: Decidability, Expressiveness, and Axiomatization}},
booktitle = {33rd International Symposium on Temporal Representation and Reasoning (TIME 2026)},
pages = {4:1--4:18},
series = {Open Access Series in Informatics (OASIcs)},
ISBN = {978-3-95977-448-2},
ISSN = {2190-6807},
year = {2026},
volume = {146},
editor = {Orlandini, AndreA and Pinchinat, Sophie},
publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
address = {Dagstuhl, Germany},
URL = {https://drops.dagstuhl.de/entities/document/10.4230/OASIcs.TIME.2026.4},
URN = {urn:nbn:de:0030-drops-277009},
doi = {10.4230/OASIcs.TIME.2026.4},
annote = {Keywords: Temporal logic, monadic Presburger arithmetic, descriptive complexity, electronic health records}
}