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[tlaplus] Re: Priming TLA+ formulas

Your formula is legal TLA+, that's why SANY (I guess that's what you call the "compiler") accepts it. TLC expects you to write

a' = 1 /\ b' = 2

because it interprets Foo' as a formula to evaluate over the next state, which it has not constructed yet. Look at chapter 14 of Specifying Systems, 
and in particular section 14.2.6 for a discussion on how TLC computes states.


On Monday, April 10, 2023 at 10:00:07 PM UTC+2 nedsr...@xxxxxxxxx wrote:
Hello again, in the example below I want to use Foo' to mean  a'=1 /\ b'=2. The compiler accepts this but TLC complains. Why is that?

Foo == a=1 /\ b=2
Init == Foo
Next == Foo /\ Foo'

Spec == Init /\ [][Next]_<<a,b>>

TLC complains 
TLC threw an unexpected exception.
This was probably caused by an error in the spec or model.
See the User Output or TLC Console for clues to what happened.
The exception was a java.lang.RuntimeException
In evaluation, the identifier a is either undefined or not an operator.
line 6, col 8 to line 6, col 8 of module test

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