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[tlaplus] Re: Why is TLA_ complaining about this? (



The logical formula in your action property must be true or false of a pair of states. The []F temporal operator is true or false of an infinite series of states.

Andrew

On Friday, April 23, 2021 at 3:38:28 PM UTC-4 ns wrote:
If I have a property of the form
    [][A => (p /\  [] (q  =>  r))]_vars                                           (1)
where A is an action and p,q,r are state predicates, I get two complaints:

Level error in applying operator $SquareAct:
The level of argument 1 exceeds the maximum level allowed by the operator.
and
=> has both temporal formula and action as arguments.

If I remove the nested [] then both complaints go away (and TLC is fine with too)
    [][A => (p /\  (q  =>  r))]_vars                                                     (2)
However, even if I replace the A with another state predicate the second complaint still remains. 
Could someone tell me where I'm going wrong. I don't recall seeing any restriction on nesting of temporal operators in the Specifying Systems book but I could have quite easily missed it. Regarding why TLC accepts the second formula (2), I assume its "nice" because its considered a Box-Action formula?

thanks

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