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

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-1

A similar formula (but with a slightly different meaning) is

y' = IF y # 0 THEN y-1 ELSE 0

Stephan

On 30 Apr 2021, at 14:39, c.burge...@gmail.com <c.burge.glasgow@xxxxxxxxx> wrote:

Hi 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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