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# Re: [tlaplus] What's wrong with this temporal formula?

 As I wrote, this is an action formula, not a temporal formula expected for properties. If you want to check that this action formula holds at all transitions, you can write[][(y=0 /\ y' = 0) \/ (y # 0 /\ y' = y-1)]_y(you may also use the tuple "vars" as the subscript if it includes y).StephanOn 30 Apr 2021, at 15:09, c.burge...@gmail.com wrote:Thanks, clearly it doesn't help when I get my logical syntaxes confused!I now have:(y=0 /\ y' = 0) \/ (y # 0 /\ y' = y-1)But when I put this as a property in TLC, I get the error:"The property ... is not correctly defined."On Friday, April 30, 2021 at 1:48:03 PM UTC+1 Stephan Merz wrote:Hello,1. "not equal" is written # in TLA+ (or /=), "~" is Boolean negation.2. I believe "->" represents implication in your formula, but it is written "=>" in  TLA+.3. The expressions on both sides of an implication should be Boolean, but the _expression_ on the right-hand side is y-1.4. The (action) formula corresponding to your informal statement can be written as\/ y' = 0\/ y # 0 /\ y' = y-1A similar formula (but with a slightly different meaning) isy' = IF y # 0 THEN y-1 ELSE 0StephanOn 30 Apr 2021, at 14:39, c.burge...@gmail.com  wrote:Hi again!I have the following temporal formula:y'= 0 \/ y ~0 -> y-1Which I hope says that the next value of y is  zero or y-1 if y is not zero.However, when I put this as a property in TLC, I get the error:Was expecting ===== or more module body, encountered '~' in Properties at line 1 and token 'y'.Obviously it's not happy with the ~ (equally unhappy with \lnot), but I'm not sure how to proceed from here!-- You received this message because you are subscribed to the Google Groups "tlaplus" group.To unsubscribe from this group and stop receiving emails from it, send an email to tlaplus+u...@xxxxxxxxxxxxxxxx.To view this discussion on the web visit https://groups.google.com/d/msgid/tlaplus/f06df008-8efa-4942-bb93-a2ebbbfe7984n%40googlegroups.com.-- You received this message because you are subscribed to the Google Groups "tlaplus" group.To unsubscribe from this group and stop receiving emails from it, send an email to tlaplus+unsubscribe@xxxxxxxxxxxxxxxx.To view this discussion on the web visit https://groups.google.com/d/msgid/tlaplus/80bd4635-9dcb-4604-a8fa-30fecd75baedn%40googlegroups.com. -- You received this message because you are subscribed to the Google Groups "tlaplus" group. To unsubscribe from this group and stop receiving emails from it, send an email to tlaplus+unsubscribe@xxxxxxxxxxxxxxxx. To view this discussion on the web visit https://groups.google.com/d/msgid/tlaplus/7E9E767C-4AA9-4068-8353-64B525E2F886%40gmail.com.