"Level error in applying operator $Tuple: The level of argument 2 exceeds the maximum level allowed by the operator"

[G.Cordier]

Hi,

When I check a constant expression with the TLA+ Tool box,
(Model > Model Checking Results : Evaluate constant expression),
I get the following error

"Level error in applying operator $Tuple:
The level of argument 2 exceeds the maximum level allowed by the operator"

For instance, if I check the below theorem T,

/// TLA Specs: BEGINNING
EXTENDS Naturals
VARIABLE h

Init == h \in (0 .. 23)
Next == h' = (h+1)%24
Spec == Init /\ [][Next]_h

THEOREM T == Spec => []Init

/// TLA SPECS: END

then I get the error message. I am really puzzled...

Could someone please explain me (1) what  does such error message mean, (2) where does the error come from, (3) how to evaluate theorems and constant expressions?

Thank you very much by advance.

Best

Gabriel

[Stephan Merz]

Hello,

constant expressions involve only constant operators, no variables, no primes, no temporal formulas. You can read more about levels of TLA formulas in chapter 16 of "Specifying Systems". You can use that functionality in order to evaluate constant expressions such as

{ 2*i+1 : i \in 0 .. 5 }

What you are really trying to do is check an invariant of a specification. To do that, tell TLC to interpret "Spec" as the specification that you are checking and "Init" as the invariant to check. For example, in the TLA+ Toolbox, create a new model, make sure that Spec appears in the "What is the behavior spec?" section of the Model Overview pane, and add Inv as an invariant in the "What to check?" section of that pane.

Hope this helps,

Stephan

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[G.Cordier]

Hello,

Thank you Stephan, this helps, definitely.

Best
Gabriel