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arxiv: 1907.06541 · v2 · pith:64ZAPVXRnew · submitted 2019-07-15 · 💻 cs.LO · cs.CR· math.LO

Time-Stamped Claim Logic

Pith reviewed 2026-05-24 21:08 UTC · model grok-4.3

classification 💻 cs.LO cs.CRmath.LO
keywords Time-Stamped Claim Logicsequent calculustrust relationsevidence reductioninconsistency removalcyber-attributiondistributed claims
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The pith

Time-Stamped Claim Logic provides a sound and complete sequent calculus that reduces evidence sets while removing inconsistencies according to trust relations.

A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.

The paper defines Time-Stamped Claim Logic for reasoning about claims collected from different sources at different times. Some claims may contradict each other, and sources vary in trustworthiness. The logic comes with a sound and complete sequent calculus that shrinks the collected evidence while eliminating inconsistencies according to the trust relations. This is useful when dealing with massive amounts of evidence, such as in cyber security investigations. A case study on cyber-attribution illustrates the practical application.

Core claim

We introduce the Time-Stamped Claim Logic including a sound and complete sequent calculus that allows one to reduce the size of the collected set of evidence and removes inconsistencies, i.e., the logic ensures that the result is consistent with respect to the trust relations considered.

What carries the argument

The sound and complete sequent calculus for Time-Stamped Claim Logic, which incorporates trust relations to manage and reduce contradictory time-stamped claims.

If this is right

  • Collected evidence from distributed sources can be systematically reduced in size.
  • Inconsistencies are removed in a way that respects the given trust relations.
  • The logic supports handling of large volumes of potentially contradictory claims.
  • The calculus is demonstrated on a cyber-attribution case study.

Where Pith is reading between the lines

These are editorial extensions of the paper, not claims the author makes directly.

  • The sequent calculus could be implemented in automated tools for real-time evidence processing.
  • Extensions might allow trust relations themselves to change over time.
  • Similar methods could apply to evidence aggregation in legal or sensor-network domains.

Load-bearing premise

Predefined trust relations between sources exist and can be applied to resolve contradictions without introducing new inconsistencies or requiring additional external validation.

What would settle it

A concrete set of time-stamped claims together with given trust relations for which the sequent calculus fails to produce a reduced and consistent result would falsify the claim.

Figures

Figures reproduced from arXiv: 1907.06541 by Cristina Sernadas, Erisa Karafili, Jo\~ao Rasga, Luca Vigan\`o.

Figure 1
Figure 1. Figure 1: Derivation of ψ1, ψ2, . . . , ψ8, δ1, δ2 → a2 : t · culpritJ C • δ2 = ∀x. x EdivergenceJ C a8 and let ∆ be the singleton set with the assertion a2 : t · culpritJ C. The derivation in [PITH_FULL_IMAGE:figures/full_fig_p008_1.png] view at source ↗
Figure 2
Figure 2. Figure 2: Subderivation of (∗) in the derivation in [PITH_FULL_IMAGE:figures/full_fig_p009_2.png] view at source ↗
Figure 3
Figure 3. Figure 3: Derivation of ψ1, δ2 → t · limitedDamagePGA U (see Subsection 7.3) BE2, which usually infects (infection) the system by exploiting the HMI vulnerabilities. SC2 states that the access to the victim system was done using phishing emails (phishEmails) and not through the exploitation of HMI vulnerabilities, because phishing emails were found in the victim system, thus there was a spear-phishing campaign (spea… view at source ↗
Figure 4
Figure 4. Figure 4: Derivation of ψ1, ψ2, δ2 → SC2 : −t · econLossPGA U (see Subsection 7.3) date of the attack. In particular, SC2 states that the attack started in Spring 2015, denoted by t 0 , as in that period there was a spear-phishing campaign, the system was infected with BE3 through the phishing emails, and a backdoor was created to the victim’s system. SA1 instead states that the attack started in December 2015, deno… view at source ↗
Figure 5
Figure 5. Figure 5: Derivation of ψ1, ψ2, δ1, δ2 → −t · econLossPGA U (see Subsection 7.3) than Bl about who is a possible culprit of PGA: SA1 EeconLoss SC2 SA1 EusedBy SA2 F1 Einfection SA2 SA1 EusedBy SC2 SA2 Einfection F2 Bl EpossibleCulprit SC1 SA1 Estarted SC2 Moreover: SC2 is the most trusted agent about how the attacker accessed the victim’s system, the economical losses, the economical motives and the limited damages;… view at source ↗
Figure 6
Figure 6. Figure 6: Derivation of ψ1, ψ2, ψ3, δ1, δ2 → SC2 : −t · econMotiveseconMotives PGA (Subsection 7.3) 7.3 The Conclusions of the Analyst In the following, we show how the analyst can use the Time-Stamped Claim Logic to draw some interesting conclusions from the collected evidence. Consider the following assertions: ψ1 = SC2 : t · limitedDamagePGA U ψ2 = SC2 :: (t · limitedDamagePGA U /−t · econLossPGA U ) ψ3 = SC2 :: … view at source ↗
Figure 7
Figure 7. Figure 7: Derivation of ψ1, ψ2, ψ3, δ1, δ2, δ3 → −t · econMotiveseconMotives PGA we can conclude SC1 : t · possibleCulpritPGA HG as can be seen in [PITH_FULL_IMAGE:figures/full_fig_p021_7.png] view at source ↗
Figure 8
Figure 8. Figure 8: Derivation of ψ4, ψ5, ψ6, ψ7, δ4, δ5, δ6 → SC1 : t · possibleCulpritPGA HG and some of the above results. However, thanks to the trust relation Bl EpossibleCulprit SC1 , which says that the analyst trusts SC1 more than Bl for what concerns the possible culprit of the attack, the analyst’s final result will discard Bl’s statement, and the analyst will conclude that the possible culprit of the attack is HG. … view at source ↗
read the original abstract

The main objective of this paper is to define a logic for reasoning about distributed time-stamped claims. Such a logic is interesting for theoretical reasons, i.e., as a logic per se, but also because it has a number of practical applications, in particular when one needs to reason about a huge amount of pieces of evidence collected from different sources, where some of the pieces of evidence may be contradictory and some sources are considered to be more trustworthy than others. We introduce the Time-Stamped Claim Logic including a sound and complete sequent calculus that allows one to reduce the size of the collected set of evidence and removes inconsistencies, i.e., the logic ensures that the result is consistent with respect to the trust relations considered. In order to show how Time-Stamped Claim Logic can be used in practice, we consider a concrete cyber-attribution case study.

Editorial analysis

A structured set of objections, weighed in public.

Desk editor's note, referee report, simulated authors' rebuttal, and a circularity audit. Tearing a paper down is the easy half of reading it; the pith above is the substance, this is the friction.

Referee Report

0 major / 2 minor

Summary. The paper defines Time-Stamped Claim Logic for reasoning about distributed time-stamped claims collected from sources with varying trust levels. It presents a sequent calculus asserted to be sound and complete that reduces the size of the evidence set and eliminates inconsistencies in a manner consistent with the given trust relations. The approach is illustrated via a concrete cyber-attribution case study.

Significance. If the soundness and completeness results hold, the logic supplies a formal mechanism for pruning contradictory evidence in large distributed collections while respecting external trust parameters. This has clear relevance to evidence management tasks in security and attribution domains. The sequent-calculus presentation and the case study together constitute a self-contained demonstration of the framework's intended use.

minor comments (2)
  1. The abstract states that the sequent calculus is sound and complete, but the manuscript would benefit from an explicit pointer (e.g., to the relevant theorem number) in the introduction so that readers can locate the proof immediately.
  2. Notation for time-stamped claims and the trust-ordering relation should be introduced with a small illustrative example before the full sequent rules are presented, to aid readability.

Simulated Author's Rebuttal

0 responses · 0 unresolved

We thank the referee for the positive summary of our paper and the recommendation for minor revision. The assessment correctly identifies the core contributions of Time-Stamped Claim Logic, the sequent calculus, and the cyber-attribution case study.

Circularity Check

0 steps flagged

No significant circularity detected

full rationale

The paper introduces a new Time-Stamped Claim Logic as a formal definition together with a sequent calculus whose soundness and completeness are established by standard proof techniques. Trust relations are external parameters supplied by the user; the calculus operates on them to prune evidence and eliminate inconsistencies without any fitted parameters, self-referential equations, or load-bearing self-citations that reduce the central result to its own inputs. The derivation chain consists of syntactic definitions, inference rules, and meta-theoretic proofs that are independent of the target conclusions; no step equates a derived quantity to a prior fit or renames an input as a prediction. This is the normal case of a self-contained logic presentation.

Axiom & Free-Parameter Ledger

0 free parameters · 2 axioms · 1 invented entities

Based solely on abstract; the work rests on standard sequent calculus properties plus new constructs for time-stamps and trust. No free parameters visible. Invented entity is the core logic itself.

axioms (2)
  • domain assumption Sequent calculus rules support soundness and completeness for the defined language
    Invoked to support the central claim of a sound and complete system
  • domain assumption Trust relations between sources are given as input and sufficient to resolve all inconsistencies
    Required for the reduction and consistency guarantee
invented entities (1)
  • Time-stamped claim no independent evidence
    purpose: To represent evidence carrying temporal and source-trust metadata
    Core modeling primitive introduced by the paper

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Reference graph

Works this paper leans on

55 extracted references · 55 canonical work pages

  1. [1]

    M. H. Almeshekah and E. H. Spafford. Planning and integrating deception into computer security defenses. In NSPW, pages 127–138. ACM, 2014

  2. [2]

    M. H. Almeshekah and E. H. Spafford. Cyber security deception. In S. Jajodia, V. S. Sub- rahmanian, V. Swarup, and C. Wang, editors, Cyber Deception: Building the Scientific Foundation, pages 23–50. Springer, 2016

  3. [3]

    S. Artemov. Explicit provability and constructive semantics. The Bulletin of Symbolic Logic, 7(1):1–36, 2001

  4. [4]

    S. Artemov. The logic of justification. The Review of Symbolic Logic, 1(4):477–513, 2008

  5. [5]

    B. Aziz. Modelling and refinement of forensic data acquisition specifications. Digital Investigation, 11(2):90–101, 2014

  6. [6]

    Baltag, B

    A. Baltag, B. Renne, and S. Smets. The logic of justified belief, explicit knowledge, and conclusive evidence. Annals of Pure and Applied Logic , 165(1):49–81, 2014

  7. [7]

    N. Beebe. Digital forensic research: The good, the bad and the unaddressed. In Ad- vances in Digital Forensics V - Fifth IFIP WG 11.9 International Conference on Digital Forensics, pages 17–36, 2009

  8. [8]

    Bucheli, R

    S. Bucheli, R. Kuznets, and T. Studer. Justifications for common knowledge. Journal of Applied Non-Classical Logics, 21(1):35–60, 2011

  9. [9]

    Caminada and D

    M. Caminada and D. M. Gabbay. A logical account of formal argumentation. Studia Logica, 93(2-3):109–145, 2009

  10. [10]

    W. A. Carnielli and A. Rodrigues. An epistemic approach to paraconsistency: a logic of evidence and truth. Synthese, in print

  11. [11]

    Analysis of the cyber attack on the Ukrainian power grid

    Defense Use Case. Analysis of the cyber attack on the Ukrainian power grid. Electricity Information Sharing and Analysis Center (E-ISAC) , 2016

  12. [12]

    P. M. Dung. On the acceptability of arguments and its fundamental role in nonmonotonic reasoning, logic programming and n-person games. Artificial Intelligence, 77(2):321–357, 1995. 26

  13. [13]

    M. Fitting. A quantified logic of evidence. Annals of Pure and Applied Logic , 152(1- 3):67–83, 2008

  14. [14]

    Fontani, T

    M. Fontani, T. Bianchi, A. De Rosa, A. Piva, and M. Barni. A framework for decision fu- sion in image forensics based on Dempster-Shafer theory of evidence. IEEE Transactions on Information Forensics and Security , 8(4):593–607, 2013

  15. [15]

    D. M. Gabbay. Fibring argumentation frames. Studia Logica, 93(2-3):231–295, 2009

  16. [16]

    R. K. Goutam. The problem of attribution in cyber security. International Journal of Computer Applications, Foundation of Computer Science , 131(7):34–36, 2015

  17. [17]

    J. Y. Halpern and R. Pucella. A logic for reasoning about evidence. Journal of Artificial Intelligence Research, 26:1–34, 2006

  18. [18]

    On digital image trustworthiness

    Donghui Hu, Xiaotian Zhang, Yuqi Fan, Zhong-Qiu Zhao, Lina Wang, Xintao Wu, and Xindong Wu. On digital image trustworthiness. Applied Soft Computing , 48:240 – 253, 2016

  19. [19]

    Karafili, M

    E. Karafili, M. Cristani, and L. Vigan` o. A formal approach to analyzing cyber-forensics evidence. In Proceedings of ESORICS 2018, Part I , pages 281–301, 2018

  20. [20]

    Karafili, L

    E. Karafili, L. Wang, A. C. Kakas, and E. Lupu. Helping forensic analysts to attribute cyber-attacks: An argumentation-based reasoner. In PRIMA, volume 11224, pages 510–

  21. [21]

    Kokkinis, Z

    I. Kokkinis, Z. Ognjanovi´ c, and T. Studer. Probabilistic justification logic. In Logical Foundations of Computer Science , volume 9537 of Lecture Notes in Computer Science , pages 174–186. Springer, 2016

  22. [22]

    J. Lurie. Probabilistic justification logic. Philosophies, 3(1):2, 2018

  23. [23]

    Rasga, A

    J. Rasga, A. Sernadas, C. Sernadas, and L. Vigan` o. Fibring labelled deduction systems. Journal of Logic and Computation , 12(3):443–473, 2002

  24. [24]

    Rasga, C

    J. Rasga, C. Sernadas, and A. Sernadas. A roadmap to decidability. In The Road to Universal Logic, pages 423–445. Springer, 2015

  25. [25]

    Sernadas, J

    A. Sernadas, J. Rasga, and C. Sernadas. On probability and logic. Portugaliae Mathe- matica, 74(4):267–313, 2017

  26. [26]

    Sernadas, J

    C. Sernadas, J. Rasga, and A. Sernadas. Preservation of Craig interpolation by the product of matrix logics. Journal of Applied Logic , 11(3):328–349, 2013

  27. [27]

    van Benthem, D

    J. van Benthem, D. Fern´ andez-Duque, and E. Pacuit. Evidence logic: a new look at neighborhood structures. In Advances in Modal Logic, volume 9, pages 97–118. College Publications, London, 2012

  28. [28]

    van Benthem and E

    J. van Benthem and E. Pacuit. Logical dynamics of evidence. In Logic, Rationality, and Interaction, volume 6953 of Lecture Notes in Computer Science , pages 1–27. Springer, 2011. 27

  29. [29]

    van Dirmarsch, W

    H. van Dirmarsch, W. van der Hoek, and B. Kooi. Dynamic Epistemic Logic. Springer, 2008

  30. [30]

    D. A. Wheeler and G. N. Larsen. Techniques for cyber attack attribution. Technical report, Institute for Defense Analyses Alexandria VA, 2003. A Some Proofs of Sections 5 and 6 Proposition A.1 (a.k.a. Proposition 5.2) The rules of the sequent calculus are sound. Proof: It is quite straightforward to see that the rules Ax, Cut, ER, ES and ET are sound. (EC...

  31. [31]

    (a) Assume that t1∼= t2∈ ΨL

    ψ is t1∼= t2. (a) Assume that t1∼= t2∈ ΨL. Then ( t1, t2)∈∼=IH and so IH ρ⊩ t1∼= t2. (b) Assume that t1∼= t2∈ ΨR. Then ( t1, t2)∈∼=IH and so IH ρ̸⊩ t1∼= t2

  32. [32]

    (a) Assume that a1⊴p a2∈ ΨL

    ψ is a1⊴p a2. (a) Assume that a1⊴p a2∈ ΨL. Then ( a1, a2)∈⊴IH p and so IH ρ⊩ a1⊴p a2. (b) Assume that a1⊴p a2∈ ΨR. Then ( a1, a2) /∈⊴IH p and so IH ρ̸⊩ a1⊴p a2

  33. [33]

    ψ is∀x. x⊴p a. (a) Assume that ∀x. x⊴p a∈ ΨL. Then for each a1∈ X′ A we have a1⊴p a∈ ΨL. Hence, IH ρ⊩ a1⊴p a for each a1∈ DA and so Iρ⊩∀x. x⊴p a. (b) Assume that ∀x. x⊴p a∈ ΨR. Then there is a′∈ X′ A such that a′⊴p a∈ ΨR. Therefore, Iρ̸⊩ a′⊴p and so Iρ̸⊩∀x. x⊴p a

  34. [34]

    (a) Assume that a : t· p∈ ΨL

    ψ is a : t· p. (a) Assume that a : t· p∈ ΨL. Then V (p, a, t) = 1 and IH ρ⊩ a : t· p. (b) Assume that a : t· p∈ ΨR. Then V (p, a, t)∈{ 0, 1 2} and so IH ρ̸⊩ a : t· p

  35. [35]

    (a) Assume that a :−(t· p)∈ ΨL

    ψ is a :−(t· p). (a) Assume that a :−(t· p)∈ ΨL. Then V (p, a, t) = 0. Hence IH ρ⊩ a :−(t· p). (b) Assume that a :−(t· p)∈ ΨR. Then V (p, a, t)∈{ 1, 1 2} and so IH ρ̸⊩ a :−(t· p)

  36. [36]

    (a) Assume that a : φ∈ ΨL

    ψ is a : φ. (a) Assume that a : φ∈ ΨL. Then, for each a′ ∈ X′ A either a⊴var(φ) a′ ∈ ΨR or a′ :−φ∈ ΨR. Hence, by the induction hypothesis, for each a′∈ X′ A either IH ρ̸⊩ a⊴var(φ)a′ or IH ρ̸⊩ a′ :−φ. Hence for each a′∈ X′ A if IH ρ⊩ a⊴var(φ)a′ then IH ρ̸⊩ a′ :−φ. Let ρ′ be an assignment such that ρ′≡A′ b ρ and IH ρ′⊩ a⊴var(φ) b. Thus IH ρ⊩ a⊴var(φ) ρ′(b)....

  37. [37]

    30 (a) Assume that φ∈ ΨL

    ψ is φ∈ KP . 30 (a) Assume that φ∈ ΨL. Then there is a′∈ X′ A such that a′ : φ, a′ : φ∈ ΨL and for every a∈ X′ A either a :−φ∈ ΨR or a : −φ∈ ΨR. Thus, by the induction hypothesis, there is a′ ∈ X′ A such that IH ρ⊩ a′ : φ and IH ρ⊩ a′ : φ and for each a∈ X′ A either IH ρ̸⊩ a :−φ or IH ρ̸⊩ a : −φ. We now show that IH ρ⊩ φ. Let ρ′ ≡A′ b ρ be such that IH ρ′...

  38. [38]

    ψ is a :: (φ1, . . . , φn/φ). (a) Assume that a :: (φ1, . . . , φn/φ)∈ ΨL. Then either φi∈ ΨR for some i = 1, . . . , n or a : φ∈ ΨL. Then, by the induction hypothesis, either IH ρ̸⊩ φi for some i = 1, . . . , n or IH ρ⊩ a : φ. Therefore, IH ρ⊩ a :: (φ1, . . . , φn/φ). (b) Assume that a :: (φ1, . . . , φn/φ)∈ ΨR. Then if φ1, . . . , φn∈ ΦL then a : φ∈ ΨR....

  39. [39]

    Assume by contradiction that β∈ ΨL and β∈ ΨR

    Either β /∈ ΨL or β /∈ ΨR where β is of the form a : φ, t1∼= t2 and a1⊴p a2. Assume by contradiction that β∈ ΨL and β∈ ΨR. Hence, there are 1 ≤ i, j≤ n such that β∈ Γ′ i and β∈ ∆′ j. Observe that any rule preserves β. Therefore, β∈ Γ′ n∩ ∆′ n and so Γ′ n→ ∆′ n is an axiom contradicting the hypothesis that the branch is open

  40. [40]

    Assume, by contradiction, that β is not in Ψ L∪ ΨR

    Either β∈ ΨL or β∈ ΨR where β is of the form a : φ, t1∼= t2 and a1⊴p a2. Assume, by contradiction, that β is not in Ψ L∪ ΨR. Consider the branch Γ ′ 1→ ∆′ 1··· Γ′ n→ ∆′ n Γ′ n→ ∆′ n, β using the cut rule in the last step. Observe that this branch is still analytical. Indeed β does not occur in ( iR)n and no fresh variables are involved. Hence we get a con...

  41. [41]

    Immediate by rule (ER) since the branch is open

    t∼= t /∈ ΨR. Immediate by rule (ER) since the branch is open. Similarly for ⊴p

  42. [42]

    Suppose that t1∼= t2∈ ΨL

    If t1∼= t2∈ ΨL then t2∼= t1 /∈ ΨR. Suppose that t1∼= t2∈ ΨL. Then if t2∼= t1∈ ΨR we could conclude that the branch was not open using rule (ES)

  43. [43]

    Suppose that t1∼= t2, t2∼= t3∈ ΨL

    If t1 ∼= t2, t2 ∼= t3 ∈ ΨL then t1 ∼= t3 /∈ ΨR and similarly for ⊴p. Suppose that t1∼= t2, t2∼= t3∈ ΨL. Then if t1∼= t3∈ ΨR we could conclude that the branch was not open using rule (ET)

  44. [44]

    Suppose that t1∼= t2, [a : φ]t1 t2∈ ΨL

    If t1∼= t2, [a : φ]t1 t2∈ ΨL then a : φ /∈ ΨR. Suppose that t1∼= t2, [a : φ]t1 t2∈ ΨL. Then if a : φ∈ ΨR we could conclude that the branch was not open using rule (EC)

  45. [45]

    The proof is similar to the one of (6)

    If a1⊴p a2, a2⊴p a1, [a : φ]a1 a2∈ ΨL then a : φ /∈ ΨR. The proof is similar to the one of (6)

  46. [46]

    x⊴p a ∈ ΨR then there is a′ ∈ X′ A such that a′⊴p a ∈ ΨR

    If ∀x. x⊴p a ∈ ΨR then there is a′ ∈ X′ A such that a′⊴p a ∈ ΨR. Assume that ∀x. x⊴p a∈ ΨR. Suppose, by contradiction, that for every a′∈ X′ A, a′⊴p a /∈ ΨR. Then, rule (AMR) was not applied to ∀x. x⊴p a and so∀x. x⊴p a∈ ∆′ n. Consider the branch Γ′ 1→ ∆′ 1··· Γ′ n→ ∆′ n Γ′ n→ (∆′ n\{∀ x. x⊴p a}), b⊴p a using in the last step the rule (AMR) where b is not...

  47. [47]

    x⊴p a∈ ΨL then a1⊴p a∈ ΨL for each a1∈ X′ A

    If ∀x. x⊴p a∈ ΨL then a1⊴p a∈ ΨL for each a1∈ X′ A. Assume that ∀x. x⊴p a∈ ΨL. Suppose, by contradiction, that there is a1∈ X′ A such that a1⊴p a /∈ ΨL. Observe that ∀x. x⊴p a is in Γ′ n. Consider the branch Γ′ 1→ ∆′ 1··· Γ′ n→ ∆′ n a1⊴p a, Γ′ n→ ∆′ n using in the last step the rule (AML). Observe that this branch is still analytical. So the original bran...

  48. [48]

    Suppose that a : φ∈ ΨL

    If a : φ∈ ΨL then a :−φ∈ ΨR. Suppose that a : φ∈ ΨL. Assume, by contradiction that a :−φ /∈ ΨR. Consider the branch Γ′ 1→ ∆′ 1··· Γ′ n→ ∆′ n Γ′ n→ ∆′ n, a :−φ using in the last step the rule (NS). Observe that this branch is still analytical. Indeed a :−φ does not occur in (iR)n and no fresh variables are involved. Hence we get a contradiction since the g...

  49. [49]

    The proof is similar to one of (10)

    If t1∼= t2, a :−(t1· p)∈ ΨR then a : t2· p∈ ΨR. The proof is similar to one of (10)

  50. [50]

    Assume that a : φ∈ ΨR

    If a : φ∈ ΨR then, there is a′∈ X′ A such that a⊴var(φ) a′, a′ :−φ∈ ΨL. Assume that a : φ∈ ΨR. Suppose, by contradiction, that for every a′∈ X′ A either a⊴var(φ) a′ /∈ ΨL or a′ :−φ /∈ ΨL. In both cases, rule (SCR) was not applied to a : φ. Then a : φ is in ∆′ n. Consider the branch Γ′ 1→ ∆′ 1··· Γ′ n→ ∆′ n a⊴var(φ) b, b :−φ, Γ′ n→ (∆′ n\{ a : φ}) using in...

  51. [51]

    Assume that a : φ∈ ΨL

    If a : φ∈ ΨL then, for each a′ ∈ X′ A either a⊴var(φ) a′ ∈ ΨR or a′ :−φ∈ ΨR. Assume that a : φ∈ ΨL. Suppose, by contradiction, that there is a′∈ X′ A such that a⊴var(φ) a′ /∈ ΨR and a′ :−φ /∈ ΨR. Observe that a : φ is in Γ′ n. Consider the branch Γ′ 1 → ∆′ 1··· Γ′ n → ∆′ n Γ′ n → ∆′ n, a⊴var(φ) a′ using in the last step the rule (SCL). Observe that this b...

  52. [52]

    Suppose that φ∈ ΨR

    If φ∈ ΨR then either there exists a′∈ X′ A such that a′ :−φ, a′ : −φ∈ ΨL or for each a∈ X′ A either a : φ∈ ΨR or a : φ∈ ΨR. Suppose that φ∈ ΨR. Assume, by contradiction, that the thesis does not hold. Then, φ∈ ∆′ n since rule (SKR) was not applied to φ in the branch. Consider the branch Γ ′ 1→ ∆′ 1··· Γ′ n→ ∆′ n b :−φ, b : −φ, Γ′ n → ∆′ n using in the las...

  53. [53]

    Assume that φ∈ ΨL

    If φ∈ ΨL then there is a′∈ X′ A such that a′ : φ, a′ : φ∈ ΨL and for each a∈ X′ A either a :−φ∈ ΨR or a : −φ∈ ΨR. Assume that φ∈ ΨL. Suppose, by contradiction and with no loss of generality, that for every a′∈ X′ A, either a′ : φ /∈ ΨL or a′ : φ /∈ ΨL. Then rule (KL) was not applied in the branch to φ. Hence, φ is in Γ′ n. Consider the branch Γ′ 1→ ∆′ 1··...

  54. [54]

    , φn/φ)∈ ΨR then if φ1,

    If a :: ( φ1, . . . , φn/φ)∈ ΨR then if φ1, . . . , φn∈ ΨL then a : φ∈ ΨR. Assume that a :: ( φ1, . . . , φn/φ)∈ ΨR and φ1, . . . , φn ∈ ΨL. Assume, by contradiction, that a : φ /∈ ΨR. Then rule (CR1) was not applied in the branch to a :: (φ1, . . . , φn/φ). Hence, a :: (φ1, . . . , φn/φ) is in ∆′ n. Consider the branch Γ′ 1→ ∆′ 1··· Γ′ n→ ∆′ n φ1, . . . ...

  55. [55]

    , φn/φ)∈ ΨL then either φi∈ ΨR for some i = 1 ,

    If a :: ( φ1, . . . , φn/φ)∈ ΨL then either φi∈ ΨR for some i = 1 , . . . , n or a : φ∈ ΨL. Suppose that a :: ( φ1, . . . , φn/φ) ∈ ΨL. Assume, by contradiction, that φi /∈ ΨR for every i = 1 , . . . , n and a : φ /∈ ΨL. Then rule (CR2) was not applied in the branch to a :: (φ1, . . . , φn/φ). Hence, a :: (φ1, . . . , φn/φ) is in Γ′ n. Consider the branch...