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Re: [tlaplus] Why does this liveness property not work?



Hmmm, I'm running it from the command line and it does report an error regardless of whether ASCII or Unicode is used.

Andrew

On Monday, October 7, 2024 at 5:35:14 PM UTC-4 Igor Konnov wrote:
It does not report any liveness violation in the TLA+ Toolbox for me
(using the ASCII version).

--
Igor

On Thu, Oct 3, 2024 at 4:47 PM Stephan Merz <stepha...@xxxxxxxxx> wrote:
>
> Interesting observation. I notice that TLC (correctly) verifies the following variants of the property:
>
> Liveness == <>[](x = 5)
> Liveness == (x = 1) /\ <>[](x = 5)
> Liveness == (x = 0) => <>[](x = 0)
>
> Stephan
>
> On 3 Oct 2024, at 16:17, Andrew Helwer <andrew...@xxxxxxxxx> wrote:
>
> Here's a simple spec with a variable x that counts from 1 to 5 then stutters at 5 forever:
>
> ---- MODULE Test ----
> EXTENDS Naturals
> VARIABLE x
> Init ≜ x = 1
> Next ≜
> IF x = 5 THEN UNCHANGED x
> ELSE x' = x + 1
> Spec ≜ Init ∧ □[Next]_x ∧ WF_x(Next)
> Liveness ≜ (x = 1) ⇒ ◇□(x = 5)
> ====
>
> However, when I try to check property Liveness with TLC I get this error:
>
> Starting... (2024-10-03 10:15:19)
> Implied-temporal checking--satisfiability problem has 1 branches.
> Computing initial states...
> Finished computing initial states: 1 distinct state generated at 2024-10-03 10:15:19.
> Error: Temporal properties were violated.
>
> Error: The following behavior constitutes a counter-example:
>
> State 1: <Initial predicate>
> x = 1
>
> 2 states generated, 2 distinct states found, 1 states left on queue.
> The depth of the complete state graph search is 2.
> Finished in 00s at (2024-10-03 10:15:19)
>
> Why is this?
>
> Andrew
>
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