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*From*: "c.burge...@xxxxxxxxx" <c.burge.glasgow@xxxxxxxxx>*Date*: Fri, 30 Apr 2021 07:04:12 -0700 (PDT)*References*: <f06df008-8efa-4942-bb93-a2ebbbfe7984n@googlegroups.com> <09E12A1A-7A9E-4A1D-9B43-7048C57AE425@gmail.com> <80bd4635-9dcb-4604-a8fa-30fecd75baedn@googlegroups.com> <7E9E767C-4AA9-4068-8353-64B525E2F886@gmail.com> <4aff7107-898f-426e-a3a2-5c49e2583302n@googlegroups.com>

Thanks again! I'm afraid that my learning style is to dive straight in and ask questions when I mess up. You have been so helpful, I really appreciate it.

On Friday, April 30, 2021 at 2:46:46 PM UTC+1 Stephan Merz wrote:

P.S.: I realize that I was imprecise in my answer. If you want to check that your action formula holds at all transitions of a system whose variables are contained in the tuple vars, you should write[][(y=0 /\ y' = 0) \/ (y # 0 /\ y' = y-1)]_varsHowever, if you want to check that the formula is true for all transitions that change y, you should write[][(y=0 /\ y' = 0) \/ (y # 0 /\ y' = y-1)]_yStephanOn Friday, April 30, 2021 at 3:17:44 PM UTC+2 Stephan Merz wrote: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 <c.burge...@xxxxxxxxx> 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 0StephanHi again!

I have the following temporal formula:y'= 0 \/ y ~0 -> y-1

Which 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!--

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**References**:**[tlaplus] What's wrong with this temporal formula?***From:*c.burge...@xxxxxxxxx

**Re: [tlaplus] What's wrong with this temporal formula?***From:*Stephan Merz

**Re: [tlaplus] What's wrong with this temporal formula?***From:*c.burge...@xxxxxxxxx

**Re: [tlaplus] What's wrong with this temporal formula?***From:*Stephan Merz

**Re: [tlaplus] What's wrong with this temporal formula?***From:*Stephan Merz

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