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First page of Proofs Without Nominals: Gödel's Ontological Argument, its Shallow Embedding, and the Open Questions of the Monatshefte Notes

Proofs Without Nominals: Gödel's Ontological Argument, its Shallow Embedding, and the Open Questions of the Monatshefte Notes

Christoph Benzmüller

cs.LO Sep 28, 2026 · v5 cs.AI math.LO
All results are verified in Lean 4 alongside Isabelle/HOL, including a 30-module Lean port of the Notes, a proof-term audit detector, and a kernel-checked countermodel.
The shallow embedding of higher-order modal logic in classical higher-order logic, used in Benzmüller and Scott's Notes on Gödel's and Scott's variants of the ontological argument, reaches beyond the modal object language: its quantifiers range over domains containing the nominals and satisfaction operators of hybrid logic. A proof using one proves a theorem of the embedding, not necessarily of the modal logic. Whether a result is one of the modal logic can be settled by replaying it in an explicit calculus, or, more cheaply and for all results at once, by analysing what the embedding's proofs substitute. Every statement the Notes prove has a proof in the embedding substituting nothing outside the object language, 294 of them explicit. The Notes' own proofs substitute none either; what it flags are terms a prover introduced. A soundness theorem over general models closed under the object language, and a sentence of that language the embedding proves but which fails in such a model, fix what the certificate says. The Notes' three open questions are settled too, without nominals, but by the empty instance of the conjunction axiom, too cheaply to convince. Generalised to Gödel's "any number of summands", the axiom covers the empty conjunction and the singleton. This article restricts it to at least two different conjuncts, a non-degenerate reading of Gödel's footnote, and settles them again without nominals. In effect only the empty conjunction is excluded; the singleton comes back with the other axioms. In one variant the restriction refutes the possible existence of a God-like being; the answers return, with no side condition, once the Notes' non-emptiness clause is confined to Gödel's essence. Every theorem here is verified in Isabelle/HOL and independently in Lean 4, the separating model in its propositional part; the countermodels are Nitpick's, checked by the build.

The shallow embedding of higher-order modal logic in HOL, used in Benzmüller and Scott's Notes on Gödel's ontological argument, admits hybrid-logic terms such as nominals. A proof that uses them proves a theorem of the embedding but not necessarily of the modal logic. The Notes also leave three open questions.

A 'hybrid-free' criterion is defined: every term a proof substitutes must belong to the modal object language. A detector checks this on proof terms, reconstructed in Isabelle/HOL and read directly from a 30-module Lean 4 port. The open questions are settled without nominals. The generalised conjunction axiom is then restricted to at least two distinct conjuncts, and the results are re-derived under this reading. Countermodels come from Nitpick, and the variant-3 countermodel is also written out and kernel-checked in Lean 4.

Every statement the Notes prove has a hybrid-free proof. The Lean port's 294 proof facts are all certified, and 403 of the 427 Isabelle facts are certified outright. The three open questions are answered in K without nominals, both under the unrestricted axiom (via its empty instance) and under the two-conjunct restriction. In one variant the restriction refutes the possible existence of a God-like being, unless the non-emptiness clause is confined to Gödel's essence.