REVIEW 3 major objections 4 minor 53 references
SC-TPTP: An Extension of the TPTP Derivation Format for Sequent-Based Calculus
T0 review · 3 major / 4 minor · reviewed 2026-08-06 · deepseek-v4-flash
Pith's one-line read The paper specifies SC-TPTP, an extension of the TPTP derivation format that makes sequent-calculus proofs from automated provers mechanically checkable and exportable to Coq.
desk verdict SC-TPTP is a sensible, well-scoped proposal for a sequent-proof interchange format; the format deserves referee time, but the Coq export is not yet shown sound. read the letter →
The pith
A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.
The reading
What carries the argument
The machinery is the two-level derivation-step system. Level 1 is a fixed set of thirty rules whose parameters are indices into the sequent, so checking a step reduces to comparing sets of formulas, and level 2 is an extensible set of advanced steps for which an elimination algorithm produces a level 1 derivation. The proof-producing e-graph, an equivalence-class data structure for terms under equalities and congruence, is the object that turns a congruence-closure justification into explicit equality edges and, recursively, into substitution proofs.
What would settle it
A concrete test is to run the library's Coq export on level 1 SC-TPTP proofs of classically valid but intuitionistically invalid sequents such as Peirce's formula and check whether the generated theorem, after stripping the double-negation encoding, is provably equivalent to the original sequent for every rule; the paper's own displayed Drinker theorem is double-negated, so the soundness of that encoding for general proofs is the crux.
Extended reading notes
Core claim
The central claim is that a proof format can be faithful to mathematical tradition and still mechanically checkable if it pins down the meaning of every derivation step. SC-TPTP derivations are lists of TPTP-annotated statements whose formulas may be sequents, and each inference names a rule from a fixed table together with parameters, mostly indices, that make verification a set-comparison check rather than a search. Level 1 rules cover structural rules, left and right introduction of connectives and quantifiers, negated forms, and equality; level 2 rules, here negation normal form, simultaneous substitution, and congruence, are justified by elimination algorithms that unfold them into level 1 derivations. The implemented pipeline lets Lisa pose a conjecture, have Goéland return an SC-TPTP proof, check it, unfold congruence steps using an e-graph with an explain method, and export the result to Coq.
Load-bearing premise
The load-bearing assumption is that the Coq translation is sound: every SC-TPTP rule, including the double-negated and inverted versions used because Coq is intuitionistic, is faithfully represented by the supplied Coq lemmas, so a Coq-accepted proof really proves the original sequent.
Editorial extensions
If this is right
- If SC-TPTP is adopted, every sequent-based tool needs only one SC-TPTP import and one export, replacing pairwise translation between every pair of systems.
- Automated theorem prover answers for first-order problems can be verified unambiguously, since each step carries enough parameters to be checked without inference.
- Users of Lisa can call Goéland as a proof-producing tactic and obtain proofs that are reconstructed inside Lisa's kernel.
- Sequent-style proofs can be exported to Coq, and level 2 steps such as congruence can be eliminated into level 1 steps, making advanced ATP reasoning digestible for proof assistants.
- The format is extensible by design: level 2 rules such as NNF are anticipated, so tools can keep their native high-level steps and eliminate only what their target cannot consume.
Reading between the lines
- Beyond the paper, the same two-level design would likely extend to typed first-order logic: adding types to the rule parameters would make some checks more involved but would not change the set-comparison principle.
- Beyond the paper, the Coq export could be turned into a fully verified translation by mechanically proving that the double-negation and inversion lemmas used for right and left rules are logically equivalent to the original sequent rules.
- Beyond the paper, adding deskolemization as a level 2 step, as the conclusion suggests, would allow tableaux proofs with on-the-fly Skolem terms to be unfolded into level 1 derivations and would remove a major obstacle to importing such proofs.
- Beyond the paper, the DRAT experience in SAT suggests that the main barrier for SC-TPTP is adoption rather than expressiveness, so an independent lightweight checker built by a third party would be a natural next step to build trust in the format.
Editorial analysis
A structured set of objections, weighed in public.
Referee Report
Summary. The paper proposes SC-TPTP, an extension of the TPTP derivation format intended for sequent-based first-order logic proofs. It defines two levels of derivation steps: 30 level-1 rules (structural, left/right introduction, left-negation, and equality rules) and three level-2 steps (NNF, congruence, and simultaneous substitution), with sequents interpreted as sets of formulas. The paper also describes a Scala library that parses, prints, checks, unfolds congruence steps, and exports proofs to Coq, together with an integration in which the Lisa proof assistant queries the Goéland ATP and imports SC-TPTP proofs. The central claims are that the format is precise, mechanically checkable, and interoperable, and that the provided tools realize these properties.
Significance. The proposal addresses a real interoperability need and has the virtue of building on the widely used TPTP syntax. The set-based semantics and explicit per-rule parameters simplify checking, and the public implementation, the proof-producing e-graph, and the working Lisa--Goéland integration are concrete artifacts that give the paper practical weight. If the soundness gaps identified below are resolved, SC-TPTP could become a useful common format for exchanging first-order sequent proofs. The level-1 rule set is standard, but the paper currently lacks the formal translation and soundness theorems needed to substantiate the Coq-export contribution and to guarantee that the format itself is sound as specified.
major comments (3)
- [Section 4.1, Examples 4.1-4.5] The Coq export is not defined as a translation on arbitrary SC-TPTP sequents and proofs. The displayed `Theorem drinker` proves `~(~(exists X, d X -> forall Y, d Y))`, while the original SC-TPTP conjecture in Example 3.2 is the positive formula `(? [X] : d(X) => (! [Y] : d(Y)))`. The paper does not state that exported proofs concern double-negated statements, does not list the classical axioms (e.g., `NNPP`, `classic`) on which the generated Coq scripts depend, and does not explain how multi-formula succedents, `cut`, or the `_s` inversion lemmas are composed into a full proof translation. Without a soundness statement relating SC-TPTP provability to Coq provability under the described translation, the contribution "export them into Coq files" is unverified.
- [Section 3.2, Tables 2 and 4] The `leftEx` and `leftNotAll` rules omit the eigenvariable (freshness) side condition. In standard LK, the rule `Γ, A(y) ⊢ Δ ⇒ Γ, ∃x.A(x) ⊢ Δ` is sound only when `y` does not occur free in `Γ, Δ`; the same freshness condition is required for `leftNotAll`. The surrounding text in Section 3.2 mentions a freshness check only for `rightAll` (step s3), so a checker implementing the tables literally would accept unsound derivations. This is a soundness gap in the proposed format itself and must be fixed in the rule definitions and in the checker.
- [Section 4.2] The e-graph-based unfolding of `congruence` steps is described only informally. No theorem states that the `explain` method always terminates, that the returned equality path is acyclic, or that its recursive expansion produces a valid sequence of level-1 `leftSubst`/`rightSubst` steps preserving the original sequent. Since eliminating level-2 steps in favor of low-level steps is a stated contribution, the unfolding procedure needs a precise correctness invariant and a proof that the constructed level-1 proof is well-formed.
minor comments (4)
- [Table 4] The parameter descriptions for `leftNotEx` and `leftNotAll` say the index points to the formula "on the right" of the conclusion; both rules are left-introduction rules, so this should read "on the left".
- [Example 3.2 vs. Table 4] Example 3.2 uses the rule name `leftNotForall`, while Table 4 names the same rule `leftNotAll`. The names should be harmonized and the example should parse against the published rule set.
- [Section 3.2, leftSubst example] The `leftSubst` derivation example appears to refer to `s1` as its own premise and contains a malformed parameter list (an extra closing parenthesis after `$fot(Z))`). It should refer to the axiom `a1` and use correct SC-TPTP syntax.
- [Section 3.2, completeness claim] The statement that the 30 rules are "complete for first order logic with equality" is asserted without proof or citation; since the paper is primarily about a format rather than a new calculus, this claim should be backed by a reference or softened to "complete for the usual LK-style presentation".
Circularity Check
No significant circularity: SC-TPTP is a proposed format with independent rule tables and a checker; the Coq export gap is a correctness concern, not a circular derivation.
full rationale
The paper's central contribution is a specification of an extension to the TPTP derivation format, not an empirically calibrated prediction or a theorem derived from prior work by the same authors. The SC-TPTP level 1 and level 2 rules are explicitly enumerated in Tables 1 through 6 with stated semantics, and the library is described as containing a parser, printer, and proof checker for the format. The use of the authors' own Goéland and Lisa systems is integration context: the format is implemented as import/export in those tools, but the format's definition does not reduce to those implementations. The Coq export section claims a 'one-to-one mapping' between SC-TPTP rules and Coq lemmas and illustrates it with examples; the absence of a formal soundness statement for that translation is a verification gap or correctness risk, not a circular step, because the export procedure is not an input to the definition of the format or to the validity checker. No derivation is fitted to data, and no assertion is justified solely by a self-citation chain. The paper is honest about being a 'proof of concept and a proposal to the community', and no load-bearing argument is equivalent by construction to its own inputs.
Assumptions & free parameters
assumptions (5)
- standard math The 30 level 1 inference rules are sound and complete for classical first-order logic with equality.
- domain assumption Sequents are identified with sets of formulas, so order and multiplicity of formulas are irrelevant.
- domain assumption The TPTP FOFX grammar supports sequents and free variables even though TPTP itself does not allow free variables.
- ad hoc to paper The Coq export translation, including its double-negation and inversion lemmas, preserves the provability of SC-TPTP sequents.
- ad hoc to paper The e-graph based algorithm of Section 4.2 correctly unfolds every congruence step into low-level substitution steps.
Cite this review
Pith. "Pith review of SC-TPTP: An Extension of the TPTP Derivation Format for Sequent-Based Calculus." pith.science (2026). https://pith.science/paper/FFS7AIZV
@misc{pith2026250711349,
author = {Pith},
title = {Pith review of: SC-TPTP: An Extension of the TPTP Derivation Format for Sequent-Based Calculus},
year = {2026},
howpublished = {\url{https://pith.science/paper/FFS7AIZV}},
note = {Machine review of arXiv:2507.11349}
}
read the original abstract
Motivated by the transfer of proofs between proof systems, and in particular from first order automated theorem provers (ATPs) to interactive theorem provers (ITPs), we specify an extension of the TPTP derivation text format to describe proofs in first-order logic: SC-TPTP. To avoid multiplication of standards, our proposed format over-specifies the TPTP derivation format by focusing on sequent formalisms. By doing so, it provides a high level of detail, is faithful to mathematical tradition, and cover multiple existing tools and in particular tableaux-based strategies. We make use of this format to allow the Lisa proof assistant to query the Go\'eland automated theorem prover, and implement a library of tools able to parse, print and check SC-TPTP proofs, export them into Coq files, and rebuild low-level proof steps from advanced ones.
Figures
Reference graph
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