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Prof. Dr. Jürgen Dix · Department of Informatics, TUC <strong>Multiagent</strong> <strong>Systems</strong>, WS 06/07 525/731<br />

8. Action/Time as Modalities 1. Time: LTL, CTL<br />

Linear Time Logic: Semantics<br />

Evaluating a formula ϕ in a path means to evaluate it in<br />

the first element of the path.<br />

Definition 8.2 (Semantics of LTL)<br />

λ[0 . . . ∞] |= p iff p is true at moment λ[0];<br />

λ[0 . . . ∞] |= ❥ ϕ iff λ[1 . . . ∞] |= ϕ;<br />

λ[0 . . . ∞] |= ♦ϕ iff λ[i . . . ∞] |= ϕ for some i 0;<br />

λ[0 . . . ∞] |= □ϕ iff λ[i . . . ∞] |= ϕ for all i 0;<br />

λ[0 . . . ∞] |= ϕ U ψ iff λ[i . . . ∞] |= ψ for some i ≥ 0, and<br />

λ[j . . . ∞] |= ϕ for all 0 ≤ j i.<br />

Note that:<br />

□ϕ ≡ ¬♦¬ϕ, ♦ϕ ≡ ¬□¬ϕ, ♦ϕ ≡ ⊤ U ϕ

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