I built Catelingo, a small constraint-based checker that flags semantically impossible LLM outputs, independent of likelihood, retrieval, or chain-of-thought. Many failures (temporal inconsistencies, numeric impossibilities, semantic type clashes) are fluent and high-likelihood. Catelingo reframes “semantic validity” as constraint satisfiability, not plausibility. Intentionally minimal & deterministic: - small sense-level lexicon - explicit constraint propagation (dependency-local) - verdict: SAT / UNSAT / UNKNOWN - optional degeneration rules for metaphor / domain adaptation

Paper (Zenodo): https://doi.org/10.5281/zenodo.18148498