|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).
-- 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:
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
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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