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Re: [tlaplus] Temporal operator leads to always (F ~> G): misunderstanding?
On 6/28/21 12:01 PM, Shuhao Wu wrote:
I've been trying to write a temporal property to check in TLC where I
want to know that some condition F leads to G, and G remain true for the
rest of time. This lead me to using the temporal operators ~> and 
together, in a statement in the form of F ~> G. I'm likely
misunderstanding one of these operators, as when I used TLC to check the
following simple spec, the nothing was found to be violated:
--fair algorithm leadstoalways
variables i = 1;
\* This is the temporal property to check
OneLeadsToTwo == (i = 1) ~> (i = 2)
step1: i := 2;
step2: i := 3;
step3: i := 2;
My understanding is that (i = 1) ~> (i = 2) would be true for the above
program (which is true in TLC). In the same understanding, (i = 1) ~>
(i = 2) would not be true, as the variable i changed from 1 to 2, then
away from 2, and then back to 2. This means that i = 2 is not always
true following the initial transition from i = 1 to i = 2.
What am I missing?
Leads-to (P ~> Q) is "syntactic sugar" for (P => <>Q) (see page 91
of Specifying Systems).
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