Discrete Linear Ensemble Logic

Abstract

We study the discrete point-based fragment of Ensemble Logic $\EL(\Nat)$ over the natural numbers, a logic combining displacement $φ_u$, bounded metric modalities $\boldBox_t$ and $\mdiamond_t$ with additive bounds, Boolean connectives, and first-order quantification over $\Nat$. Motivated by the need for a unified symbolic layer for biomedical knowledge with temporal, spatial, genomic, and multimodal metric content, we develop the foundational discrete theory of the formalism. We give syntax and semantics, and prove a forward embedding of $\EL(\Nat)$ over a finite proposition set $\mathcal{P}$ into first-order monadic Presburger arithmetic $\FO(\Nat,<,+;\mathcal{P})$. This embedding yields the analytical upper bounds, while a reduction from nondeterministic two-counter machines with recurring control states proves that satisfiability is $Σ^1_1$-complete and validity is dually $Π^1_1$-complete. Expressively, $\EL(\Nat)$ strictly extends the star-free $ω$-languages and is incomparable with the $ω$-regular languages: it defines the non-$ω$-regular counting language $\{a^mb^mc^md^m\mid m\geq 1\}\cdotΣ^ω$, whereas a delimited parity language remains outside the logic by classical Presburger-arithmetic lower bounds. On the proof-theoretic side, we present a sound Hilbert system $\HEL$ and establish completeness relative to monadic Presburger validity as oracle, noting that completeness relative to plain Presburger arithmetic is impossible.