What about Finite Models? Fix AP = { a } and consider the conjunction ϕ of ∀ π. ( ¬ a π ) U ( a π ∧ X G ¬ a π ) ∃ π. a π ∀ π. ∃ π ′ . F ( a π ∧ X a π ′ ) { a } ∅ ∅ ∅ ∅ ∅ ∅ ∅ · · · ∅ { a } ∅ ∅ ∅ ∅ ∅ ∅ · · · ∅ ∅ { a } ∅ ∅ ∅ ∅ ∅ · · · . . . . . . . . . . . . . . . . . . . . . . . . The unique model of ϕ is {∅ n { a } ∅ ω | n ∈ N } . Theorem There is a satisfiable HyperLTL sentence that is not satisfied by any finite set of traces. Martin Zimmermann Saarland University Logics for Hyperproperties 13/40
What about Countable Models? Theorem Every satisfiable HyperLTL sentence has a countable model. Martin Zimmermann Saarland University Logics for Hyperproperties 14/40
What about Countable Models? Theorem Every satisfiable HyperLTL sentence has a countable model. Proof W.l.o.g. ϕ = ∀ π 0 . ∃ π ′ 0 . · · · ∀ π k . ∃ π ′ k . ψ with quantifier-free ψ . Fix a Skolem function f j for every existentially quantified π ′ j . Martin Zimmermann Saarland University Logics for Hyperproperties 14/40
What about Countable Models? Theorem Every satisfiable HyperLTL sentence has a countable model. Proof W.l.o.g. ϕ = ∀ π 0 . ∃ π ′ 0 . · · · ∀ π k . ∃ π ′ k . ψ with quantifier-free ψ . Fix a Skolem function f j for every existentially quantified π ′ j . t Martin Zimmermann Saarland University Logics for Hyperproperties 14/40
What about Countable Models? Theorem Every satisfiable HyperLTL sentence has a countable model. Proof W.l.o.g. ϕ = ∀ π 0 . ∃ π ′ 0 . · · · ∀ π k . ∃ π ′ k . ψ with quantifier-free ψ . Fix a Skolem function f j for every existentially quantified π ′ j . f 0 ( t ) f k ( t , . . . , t ) t f 1 ( t , t ) · · · Martin Zimmermann Saarland University Logics for Hyperproperties 14/40
What about Countable Models? Theorem Every satisfiable HyperLTL sentence has a countable model. Proof W.l.o.g. ϕ = ∀ π 0 . ∃ π ′ 0 . · · · ∀ π k . ∃ π ′ k . ψ with quantifier-free ψ . Fix a Skolem function f j for every existentially quantified π ′ j . t Martin Zimmermann Saarland University Logics for Hyperproperties 14/40
What about Countable Models? Theorem Every satisfiable HyperLTL sentence has a countable model. Proof W.l.o.g. ϕ = ∀ π 0 . ∃ π ′ 0 . · · · ∀ π k . ∃ π ′ k . ψ with quantifier-free ψ . Fix a Skolem function f j for every existentially quantified π ′ j . · · · · · · t Martin Zimmermann Saarland University Logics for Hyperproperties 14/40
What about Countable Models? Theorem Every satisfiable HyperLTL sentence has a countable model. Proof W.l.o.g. ϕ = ∀ π 0 . ∃ π ′ 0 . · · · ∀ π k . ∃ π ′ k . ψ with quantifier-free ψ . Fix a Skolem function f j for every existentially quantified π ′ j . · · · · · · t The limit is a model of ϕ and countable. Martin Zimmermann Saarland University Logics for Hyperproperties 14/40
What about Regular Models? Theorem There is a satisfiable HyperLTL sentence that is not satisfied by any ω -regular set of traces. Martin Zimmermann Saarland University Logics for Hyperproperties 15/40
What about Regular Models? Theorem There is a satisfiable HyperLTL sentence that is not satisfied by any ω -regular set of traces. Proof Express that a model T contains.. 1. .. ( { a }{ b } ) n ∅ ω for every n . Martin Zimmermann Saarland University Logics for Hyperproperties 15/40
What about Regular Models? Theorem There is a satisfiable HyperLTL sentence that is not satisfied by any ω -regular set of traces. Proof { a } { b } { a } { b } { a } { b } ∅ ω Express that a model T contains.. 1. .. ( { a }{ b } ) n ∅ ω for every n . Martin Zimmermann Saarland University Logics for Hyperproperties 15/40
What about Regular Models? Theorem There is a satisfiable HyperLTL sentence that is not satisfied by any ω -regular set of traces. Proof { a } { b } { a } { b } { a } { b } ∅ ω Express that a model T contains.. 1. .. ( { a }{ b } ) n ∅ ω for every n . 2. .. for every trace of the form x { b }{ a } y in T , also the trace x { a }{ b } y . Martin Zimmermann Saarland University Logics for Hyperproperties 15/40
What about Regular Models? Theorem There is a satisfiable HyperLTL sentence that is not satisfied by any ω -regular set of traces. Proof { a } { b } { a } { b } { a } { b } ∅ ω Express that a model T contains.. 1. .. ( { a }{ b } ) n ∅ ω for every n . { a } { a } { b } { b } { a } { b } ∅ ω 2. .. for every trace of the form x { b }{ a } y in T , also the trace x { a }{ b } y . Martin Zimmermann Saarland University Logics for Hyperproperties 15/40
What about Regular Models? Theorem There is a satisfiable HyperLTL sentence that is not satisfied by any ω -regular set of traces. Proof { a } { b } { a } { b } { a } { b } ∅ ω Express that a model T contains.. 1. .. ( { a }{ b } ) n ∅ ω for every n . { a } { a } { b } { b } { a } { b } ∅ ω 2. .. for every trace of the form { a } { a } { b } { a } { b } { b } ∅ ω x { b }{ a } y in T , also the trace x { a }{ b } y . Martin Zimmermann Saarland University Logics for Hyperproperties 15/40
What about Regular Models? Theorem There is a satisfiable HyperLTL sentence that is not satisfied by any ω -regular set of traces. Proof { a } { b } { a } { b } { a } { b } ∅ ω Express that a model T contains.. 1. .. ( { a }{ b } ) n ∅ ω for every n . { a } { a } { b } { b } { a } { b } ∅ ω 2. .. for every trace of the form { a } { a } { b } { a } { b } { b } ∅ ω x { b }{ a } y in T , also the trace x { a }{ b } y . { a } { a } { a } { b } { b } { b } ∅ ω Martin Zimmermann Saarland University Logics for Hyperproperties 15/40
What about Regular Models? Theorem There is a satisfiable HyperLTL sentence that is not satisfied by any ω -regular set of traces. Proof { a } { b } { a } { b } { a } { b } ∅ ω Express that a model T contains.. 1. .. ( { a }{ b } ) n ∅ ω for every n . { a } { a } { b } { b } { a } { b } ∅ ω 2. .. for every trace of the form { a } { a } { b } { a } { b } { b } ∅ ω x { b }{ a } y in T , also the trace x { a }{ b } y . { a } { a } { a } { b } { b } { b } ∅ ω Then, T ∩ { a } ∗ { b } ∗ ∅ ω = {{ a } n { b } n ∅ ω | n ∈ N } is not ω -regular. Martin Zimmermann Saarland University Logics for Hyperproperties 15/40
What about Ultimately Periodic Models? Theorem There is a satisfiable HyperLTL sentence that is not satisfied by any set of traces that contains an ultimately periodic trace. Martin Zimmermann Saarland University Logics for Hyperproperties 16/40
What about Ultimately Periodic Models? Theorem There is a satisfiable HyperLTL sentence that is not satisfied by any set of traces that contains an ultimately periodic trace. One can even encode the prime numbers in HyperLTL! Martin Zimmermann Saarland University Logics for Hyperproperties 16/40
References Bernd Finkbeiner and Martin Zimmermann. The first-order logic of hyperproperties. In Proceedings of STACS 2017 . Martin Zimmermann Saarland University Logics for Hyperproperties 17/40
Outline 1. HyperLTL 2. The Models Of HyperLTL 3. HyperLTL Satisfiability 4. HyperLTL Model-checking 5. The First-order Logic of Hyperproperties 6. Conclusion Martin Zimmermann Saarland University Logics for Hyperproperties 18/40
Undecidability The HyperLTL satisfiability problem: Given ϕ , is there a non-empty set T of traces with T | = ϕ ? Theorem HyperLTL satisfiability is undecidable. Martin Zimmermann Saarland University Logics for Hyperproperties 19/40
Undecidability The HyperLTL satisfiability problem: Given ϕ , is there a non-empty set T of traces with T | = ϕ ? Theorem HyperLTL satisfiability is undecidable. Proof: By a reduction from Post’s correspondence problem. Example Blocks ( a , baa ) ( ab , aa ) ( bba , bb ) Martin Zimmermann Saarland University Logics for Hyperproperties 19/40
Undecidability The HyperLTL satisfiability problem: Given ϕ , is there a non-empty set T of traces with T | = ϕ ? Theorem HyperLTL satisfiability is undecidable. Proof: By a reduction from Post’s correspondence problem. Example Blocks ( a , baa ) ( ab , aa ) ( bba , bb ) A solution: a a a a b b b b b a a a a b b b b b Martin Zimmermann Saarland University Logics for Hyperproperties 19/40
Undecidability The HyperLTL satisfiability problem: Given ϕ , is there a non-empty set T of traces with T | = ϕ ? Theorem HyperLTL satisfiability is undecidable. Proof: By a reduction from Post’s correspondence problem. Example Blocks ( a , baa ) ( ab , aa ) ( bba , bb ) A solution: a a a a b b b b b a a a a b b b b b Martin Zimmermann Saarland University Logics for Hyperproperties 19/40
Undecidability 1. There is a (solution) trace where top matches bottom. Martin Zimmermann Saarland University Logics for Hyperproperties 20/40
Undecidability { b } { b } { a } { a } { b } { b } { b } { a } { a } ∅ ω { b } { b } { a } { a } { b } { b } { b } { a } { a } ∅ ω 1. There is a (solution) trace where top matches bottom. Martin Zimmermann Saarland University Logics for Hyperproperties 20/40
Undecidability { b } { b } { a } { a } { b } { b } { b } { a } { a } ∅ ω { b } { b } { a } { a } { b } { b } { b } { a } { a } ∅ ω 1. There is a (solution) trace where top matches bottom. 2. Every trace is finite and starts with a block or is empty . Martin Zimmermann Saarland University Logics for Hyperproperties 20/40
Undecidability { b } { b } { a } { a } { b } { b } { b } { a } { a } ∅ ω { b } { b } { a } { a } { b } { b } { b } { a } { a } ∅ ω 1. There is a (solution) trace where top matches bottom. 2. Every trace is finite and starts with a block or is empty . Martin Zimmermann Saarland University Logics for Hyperproperties 20/40
Undecidability { b } { b } { a } { a } { b } { b } { b } { a } { a } ∅ ω { b } { b } { a } { a } { b } { b } { b } { a } { a } ∅ ω 1. There is a (solution) trace where top matches bottom. 2. Every trace is finite and starts with a block or is empty . 3. For every non-empty trace, the trace obtained by removing the first block also exists. Martin Zimmermann Saarland University Logics for Hyperproperties 20/40
Undecidability { b } { b } { a } { a } { b } { b } { b } { a } { a } ∅ ω { b } { b } { a } { a } { b } { b } { b } { a } { a } ∅ ω 1. There is a (solution) trace where top { a } { b } { b } { b } { a } { a } ∅ ω ∅ ∅ ∅ matches bottom. { a } { a } { b } { b } { b } { a } { a } ∅ ω ∅ ∅ 2. Every trace is finite and starts with a block or is empty . 3. For every non-empty trace, the trace obtained by removing the first block also exists. Martin Zimmermann Saarland University Logics for Hyperproperties 20/40
Undecidability { b } { b } { a } { a } { b } { b } { b } { a } { a } ∅ ω { b } { b } { a } { a } { b } { b } { b } { a } { a } ∅ ω 1. There is a (solution) trace where top { a } { b } { b } { b } { a } { a } ∅ ω ∅ ∅ ∅ matches bottom. { a } { a } { b } { b } { b } { a } { a } ∅ ω ∅ ∅ 2. Every trace is finite and starts with a block or is empty . 3. For every non-empty trace, the trace obtained by removing the first block also exists. Martin Zimmermann Saarland University Logics for Hyperproperties 20/40
Undecidability { b } { b } { a } { a } { b } { b } { b } { a } { a } ∅ ω { b } { b } { a } { a } { b } { b } { b } { a } { a } ∅ ω 1. There is a (solution) trace where top { a } { b } { b } { b } { a } { a } ∅ ω ∅ ∅ ∅ matches bottom. { a } { a } { b } { b } { b } { a } { a } ∅ ω ∅ ∅ 2. Every trace is finite and starts with a block or is empty . 3. For every non-empty trace, the trace obtained by removing the first block also exists. Martin Zimmermann Saarland University Logics for Hyperproperties 20/40
Undecidability { b } { b } { a } { a } { b } { b } { b } { a } { a } ∅ ω { b } { b } { a } { a } { b } { b } { b } { a } { a } ∅ ω 1. There is a (solution) trace where top { a } { b } { b } { b } { a } { a } ∅ ω ∅ ∅ ∅ matches bottom. { a } { a } { b } { b } { b } { a } { a } ∅ ω ∅ ∅ 2. Every trace is finite and starts with a ∅ ω { b } { b } { a } { a } ∅ ∅ ∅ ∅ ∅ block or is empty . { b } { b } { b } { a } { a } ∅ ω ∅ ∅ ∅ ∅ 3. For every non-empty trace, the trace obtained by removing the first block also exists. Martin Zimmermann Saarland University Logics for Hyperproperties 20/40
Undecidability { b } { b } { a } { a } { b } { b } { b } { a } { a } ∅ ω { b } { b } { a } { a } { b } { b } { b } { a } { a } ∅ ω 1. There is a (solution) trace where top { a } { b } { b } { b } { a } { a } ∅ ω ∅ ∅ ∅ matches bottom. { a } { a } { b } { b } { b } { a } { a } ∅ ω ∅ ∅ 2. Every trace is finite and starts with a ∅ ω { b } { b } { a } { a } ∅ ∅ ∅ ∅ ∅ block or is empty . { b } { b } { b } { a } { a } ∅ ω ∅ ∅ ∅ ∅ 3. For every non-empty trace, the trace obtained by removing the first block also exists. Martin Zimmermann Saarland University Logics for Hyperproperties 20/40
Undecidability { b } { b } { a } { a } { b } { b } { b } { a } { a } ∅ ω { b } { b } { a } { a } { b } { b } { b } { a } { a } ∅ ω 1. There is a (solution) trace where top { a } { b } { b } { b } { a } { a } ∅ ω ∅ ∅ ∅ matches bottom. { a } { a } { b } { b } { b } { a } { a } ∅ ω ∅ ∅ 2. Every trace is finite and starts with a ∅ ω { b } { b } { a } { a } ∅ ∅ ∅ ∅ ∅ block or is empty . { b } { b } { b } { a } { a } ∅ ω ∅ ∅ ∅ ∅ 3. For every non-empty trace, the trace obtained by removing the first block also exists. Martin Zimmermann Saarland University Logics for Hyperproperties 20/40
Undecidability { b } { b } { a } { a } { b } { b } { b } { a } { a } ∅ ω { b } { b } { a } { a } { b } { b } { b } { a } { a } ∅ ω 1. There is a (solution) trace where top { a } { b } { b } { b } { a } { a } ∅ ω ∅ ∅ ∅ matches bottom. { a } { a } { b } { b } { b } { a } { a } ∅ ω ∅ ∅ 2. Every trace is finite and starts with a ∅ ω { b } { b } { a } { a } ∅ ∅ ∅ ∅ ∅ block or is empty . { b } { b } { b } { a } { a } ∅ ω ∅ ∅ ∅ ∅ 3. For every non-empty trace, the trace { a } ∅ ω ∅ ∅ ∅ ∅ ∅ ∅ ∅ ∅ obtained by { b } { a } { a } ∅ ω ∅ ∅ ∅ ∅ ∅ ∅ removing the first block also exists. Martin Zimmermann Saarland University Logics for Hyperproperties 20/40
Undecidability { b } { b } { a } { a } { b } { b } { b } { a } { a } ∅ ω { b } { b } { a } { a } { b } { b } { b } { a } { a } ∅ ω 1. There is a (solution) trace where top { a } { b } { b } { b } { a } { a } ∅ ω ∅ ∅ ∅ matches bottom. { a } { a } { b } { b } { b } { a } { a } ∅ ω ∅ ∅ 2. Every trace is finite and starts with a ∅ ω { b } { b } { a } { a } ∅ ∅ ∅ ∅ ∅ block or is empty . { b } { b } { b } { a } { a } ∅ ω ∅ ∅ ∅ ∅ 3. For every non-empty trace, the trace { a } ∅ ω ∅ ∅ ∅ ∅ ∅ ∅ ∅ ∅ obtained by { b } { a } { a } ∅ ω ∅ ∅ ∅ ∅ ∅ ∅ removing the first block also exists. Martin Zimmermann Saarland University Logics for Hyperproperties 20/40
Undecidability { b } { b } { a } { a } { b } { b } { b } { a } { a } ∅ ω { b } { b } { a } { a } { b } { b } { b } { a } { a } ∅ ω 1. There is a (solution) trace where top { a } { b } { b } { b } { a } { a } ∅ ω ∅ ∅ ∅ matches bottom. { a } { a } { b } { b } { b } { a } { a } ∅ ω ∅ ∅ 2. Every trace is finite and starts with a ∅ ω { b } { b } { a } { a } ∅ ∅ ∅ ∅ ∅ block or is empty . { b } { b } { b } { a } { a } ∅ ω ∅ ∅ ∅ ∅ 3. For every non-empty trace, the trace { a } ∅ ω ∅ ∅ ∅ ∅ ∅ ∅ ∅ ∅ obtained by { b } { a } { a } ∅ ω ∅ ∅ ∅ ∅ ∅ ∅ removing the first block also exists. ∅ ω ∅ ∅ ∅ ∅ ∅ ∅ ∅ ∅ ∅ ∅ ω ∅ ∅ ∅ ∅ ∅ ∅ ∅ ∅ ∅ Martin Zimmermann Saarland University Logics for Hyperproperties 20/40
Decidability Theorem ∃ ∗ -HyperLTL satisfiability is PSpace -complete. Martin Zimmermann Saarland University Logics for Hyperproperties 21/40
Decidability Theorem ∃ ∗ -HyperLTL satisfiability is PSpace -complete. Proof: Membership: Consider ϕ = ∃ π 0 . . . ∃ π k . ψ . Obtain ψ ′ from ψ by replacing each a π j by a fresh proposition a j . Then: ϕ and the LTL formula ψ ′ are equi-satisfiable. Hardness: trivial reduction from LTL satisfiability Martin Zimmermann Saarland University Logics for Hyperproperties 21/40
Decidability Theorem ∀ ∗ -HyperLTL satisfiability is PSpace -complete. Martin Zimmermann Saarland University Logics for Hyperproperties 22/40
Decidability Theorem ∀ ∗ -HyperLTL satisfiability is PSpace -complete. Proof: Membership: Consider ϕ = ∀ π 0 . . . ∀ π k . ψ . Obtain ψ ′ from ψ by replacing each a π j by a . Then: ϕ and the LTL formula ψ ′ are equi-satisfiable. Hardness: trivial reduction from LTL satisfiability Martin Zimmermann Saarland University Logics for Hyperproperties 22/40
Decidability Theorem ∃ ∗ ∀ ∗ -HyperLTL satisfiability is ExpSpace -complete. Martin Zimmermann Saarland University Logics for Hyperproperties 23/40
Decidability Theorem ∃ ∗ ∀ ∗ -HyperLTL satisfiability is ExpSpace -complete. Proof: Membership: Consider ϕ = ∃ π 0 . . . ∃ π k . ∀ π ′ 0 . . . ∀ π ′ ℓ . ψ . Let k k ϕ ′ = ∃ π 0 . . . ∃ π k � � · · · ψ j 0 ,..., j ℓ j 0 = 0 j ℓ = 0 where ψ j 0 ,..., j ℓ is obtained from ψ by replacing each occurrence of π ′ i by π j i . Then: ϕ and ϕ ′ are equi-satisfiable. Hardness: encoding of exponential-space Turing machines. Martin Zimmermann Saarland University Logics for Hyperproperties 23/40
Further Results HyperLTL implication checking: given ϕ and ϕ ′ , does, for every T , = ϕ ′ ? T | = ϕ imply T | Lemma ϕ does not imply ϕ ′ iff ( ϕ ∧ ¬ ϕ ′ ) is satisfiable. Martin Zimmermann Saarland University Logics for Hyperproperties 24/40
Further Results HyperLTL implication checking: given ϕ and ϕ ′ , does, for every T , = ϕ ′ ? T | = ϕ imply T | Lemma ϕ does not imply ϕ ′ iff ( ϕ ∧ ¬ ϕ ′ ) is satisfiable. Corollary Implication checking for alternation-free HyperLTL formulas is ExpSpace -complete. Tool EAHyper : satisfiability, implication, and equivalence checking for HyperLTL Martin Zimmermann Saarland University Logics for Hyperproperties 24/40
References Bernd Finkbeiner and Christopher Hahn. Deciding Hyperproperties. In Proceedings of CONCUR 2016 . Bernd Finkbeiner, Christopher Hahn, and Marvin Stenger. EAHyper: Satisfiability, Implication, and Equivalence Checking of Hyperproperties. In Proceedings of CAV 2017 . Martin Zimmermann Saarland University Logics for Hyperproperties 25/40
Outline 1. HyperLTL 2. The Models Of HyperLTL 3. HyperLTL Satisfiability 4. HyperLTL Model-checking 5. The First-order Logic of Hyperproperties 6. Conclusion Martin Zimmermann Saarland University Logics for Hyperproperties 26/40
Model-Checking The HyperLTL model-checking problem: Given a transition system S and ϕ , does Traces ( S ) | = ϕ ? Theorem The HyperLTL model-checking problem is decidable. Martin Zimmermann Saarland University Logics for Hyperproperties 27/40
Model-Checking Proof: Consider ϕ = ∃ π 1 . ∀ π 2 . . . . ∃ π k − 1 . ∀ π k . ψ . Rewrite as ∃ π 1 . ¬∃ π 2 . ¬ . . . ∃ π k − 1 . ¬∃ π k . ¬ ψ . Martin Zimmermann Saarland University Logics for Hyperproperties 28/40
Model-Checking Proof: Consider ϕ = ∃ π 1 . ∀ π 2 . . . . ∃ π k − 1 . ∀ π k . ψ . Rewrite as ∃ π 1 . ¬∃ π 2 . ¬ . . . ∃ π k − 1 . ¬∃ π k . ¬ ψ . By induction over quantifier prefix construct non-determinstic Büchi automaton A with L ( A ) � = ∅ iff Traces ( S ) | = ϕ . Induction start: build automaton for LTL formula obtained from ¬ ψ by replacing a π j by a j . For ∃ π j θ restrict automaton for θ in dimension j to traces of S . For ¬ θ complement automaton for θ . Martin Zimmermann Saarland University Logics for Hyperproperties 28/40
Model-Checking Proof: Consider ϕ = ∃ π 1 . ∀ π 2 . . . . ∃ π k − 1 . ∀ π k . ψ . Rewrite as ∃ π 1 . ¬∃ π 2 . ¬ . . . ∃ π k − 1 . ¬∃ π k . ¬ ψ . By induction over quantifier prefix construct non-determinstic Büchi automaton A with L ( A ) � = ∅ iff Traces ( S ) | = ϕ . Induction start: build automaton for LTL formula obtained from ¬ ψ by replacing a π j by a j . For ∃ π j θ restrict automaton for θ in dimension j to traces of S . For ¬ θ complement automaton for θ . ⇒ Non-elementary complexity, but alternation-free fragments are as hard as LTL. Martin Zimmermann Saarland University Logics for Hyperproperties 28/40
References Bernd Finkbeiner, Markus N. Rabe, and César Sánchez. Algorithms for Model Checking HyperLTL and HyperCTL ∗ . In Proceedings of CAV 2015 . Martin Zimmermann Saarland University Logics for Hyperproperties 29/40
Outline 1. HyperLTL 2. The Models Of HyperLTL 3. HyperLTL Satisfiability 4. HyperLTL Model-checking 5. The First-order Logic of Hyperproperties 6. Conclusion Martin Zimmermann Saarland University Logics for Hyperproperties 30/40
First-order Logic vs. LTL FO [ < ] : first-order order logic over signature { < } ∪ { P a | a ∈ AP } over structures with universe N . Theorem (Kamp ’68, Gabbay et al. ’80) LTL and FO [ < ] are expressively equivalent. Martin Zimmermann Saarland University Logics for Hyperproperties 31/40
First-order Logic vs. LTL FO [ < ] : first-order order logic over signature { < } ∪ { P a | a ∈ AP } over structures with universe N . Theorem (Kamp ’68, Gabbay et al. ’80) LTL and FO [ < ] are expressively equivalent. Example ∀ x ( P q ( x ) ∧ ¬ P p ( x )) → ∃ y ( x < y ∧ P p ( y )) and G ( q → F p ) are equivalent. Martin Zimmermann Saarland University Logics for Hyperproperties 31/40
First-order Logic for Hyperproperties N · · · < Martin Zimmermann Saarland University Logics for Hyperproperties 32/40
First-order Logic for Hyperproperties N · · · < · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · T · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Martin Zimmermann Saarland University Logics for Hyperproperties 32/40
First-order Logic for Hyperproperties N · · · < · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · E T · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Martin Zimmermann Saarland University Logics for Hyperproperties 32/40
First-order Logic for Hyperproperties N · · · < · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · E T · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . FO [ <, E ] : first-order logic with equality over the signature { <, E } ∪ { P a | a ∈ AP } over structures with universe T × N . Example ∀ x ∀ x ′ E ( x , x ′ ) → ( P on ( x ) ↔ P on ( x ′ )) Martin Zimmermann Saarland University Logics for Hyperproperties 32/40
First-order Logic for Hyperproperties N · · · < · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · E T · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . FO [ <, E ] : first-order logic with equality over the signature { <, E } ∪ { P a | a ∈ AP } over structures with universe T × N . Proposition For every HyperLTL sentence there is an equivalent FO [ <, E ] sentence. Martin Zimmermann Saarland University Logics for Hyperproperties 32/40
A Setback Let ϕ be the following property of sets T ⊆ ( 2 { p } ) ω : There is an n such that p / ∈ t ( n ) for every t ∈ T . Theorem (Bozzelli et al. ’15) ϕ is not expressible in HyperLTL. Martin Zimmermann Saarland University Logics for Hyperproperties 33/40
A Setback Let ϕ be the following property of sets T ⊆ ( 2 { p } ) ω : There is an n such that p / ∈ t ( n ) for every t ∈ T . Theorem (Bozzelli et al. ’15) ϕ is not expressible in HyperLTL. But, ϕ is easily expressible in FO [ <, E ] : ∃ x ∀ y E ( x , y ) → ¬ P p ( y ) Corollary FO [ <, E ] strictly subsumes HyperLTL. Martin Zimmermann Saarland University Logics for Hyperproperties 33/40
HyperFO ∃ M x and ∀ M x : quantifiers restricted to initial positions. ∃ G y ≥ x and ∀ G y ≥ x : if x is initial, then quantifiers restricted to positions on the same trace as x . Martin Zimmermann Saarland University Logics for Hyperproperties 34/40
HyperFO ∃ M x and ∀ M x : quantifiers restricted to initial positions. ∃ G y ≥ x and ∀ G y ≥ x : if x is initial, then quantifiers restricted to positions on the same trace as x . HyperFO: sentences of the form ϕ = Q M 1 x 1 . · · · Q M k x k . Q G 1 y 1 ≥ x g 1 . · · · Q G ℓ y ℓ ≥ x g ℓ . ψ Q ∈ {∃ , ∀} , { x 1 , . . . , x k } and { y 1 , . . . , y ℓ } are disjoint, every guard x g j is in { x 1 , . . . , x k } , and ψ is quantifier-free over signature { <, E } ∪ { P a | a ∈ AP } with free variables in { y 1 , . . . , y ℓ } . Martin Zimmermann Saarland University Logics for Hyperproperties 34/40
Equivalence Theorem HyperLTL and HyperFO are equally expressive. Martin Zimmermann Saarland University Logics for Hyperproperties 35/40
Equivalence Theorem HyperLTL and HyperFO are equally expressive. Proof From HyperLTL to HyperFO: structural induction. From HyperFO to HyperLTL: reduction to Kamp’s theorem. Martin Zimmermann Saarland University Logics for Hyperproperties 35/40
From HyperFO to HyperLTL ∀ x ∀ x ′ E ( x , x ′ ) → ( P on ( x ) ↔ P on ( x ′ )) Martin Zimmermann Saarland University Logics for Hyperproperties 36/40
From HyperFO to HyperLTL ∀ x ∀ x ′ E ( x , x ′ ) → ( P on ( x ) ↔ P on ( x ′ )) ∀ M x 1 ∀ M x 2 ∀ G y 1 ≥ x 1 ∀ G y 2 ≥ x 2 E ( y 1 , y 2 ) → ( P on ( y 1 ) ↔ P on ( y 2 )) Martin Zimmermann Saarland University Logics for Hyperproperties 36/40
From HyperFO to HyperLTL ∀ x ∀ x ′ E ( x , x ′ ) → ( P on ( x ) ↔ P on ( x ′ )) ∀ M x 1 ∀ M x 2 ∀ G y 1 ≥ x 1 ∀ G y 2 ≥ x 2 E ( y 1 , y 2 ) → ( P on ( y 1 ) ↔ P on ( y 2 )) x 1 �→ { on } { on } { on } · · · ∅ x 2 �→ { on } { on } · · · ∅ ∅ Martin Zimmermann Saarland University Logics for Hyperproperties 36/40
From HyperFO to HyperLTL ∀ x ∀ x ′ E ( x , x ′ ) → ( P on ( x ) ↔ P on ( x ′ )) ∀ G y 1 ≥ x 1 ∀ G y 2 ≥ x 2 E ( y 1 , y 2 ) → ( P on ( y 1 ) ↔ P on ( y 2 )) x 1 �→ { on } { on } { on } · · · ∅ x 2 �→ { on } { on } · · · ∅ ∅ Martin Zimmermann Saarland University Logics for Hyperproperties 36/40
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