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*From*: Leslie Lamport <tlaplus.ll@xxxxxxxxx>*Date*: Tue, 8 Jun 2021 12:40:15 -0700 (PDT)*References*: <f71490a1-015b-c6f0-a24f-efe11a7757e4@gmail.com> <CAM3xQxF1rK3vC7LTYFHzyHoeb28zc4=r1f2PyVXvTt65QyddZw@mail.gmail.com> <211edb41-3abe-ea5c-80a5-445d36872205@lemmster.de>

I don't know if people realize that TLC can handle:

VARIABLES x, y, a, b, c

foo == <<x, y>>

bar == <<a, foo>>

boo == <<b, c>>

...

/\ UNCHANGED <<bar, d, boo>>

On Tuesday, June 8, 2021 at 12:13:42 PM UTC-7 Markus Alexander Kuppe wrote:

On 06.06.21 15:57, Isaac DeFrain wrote:

>

> To manage the amount of names I have to write following UNCHANGED, I

> usually write several /inclusive/ and /exclusive/ variable tuples; e.g.

> say we have the variables x1, x2, ..., xN and I have a few actions which

> change only x1 and x2 and leave x3, ..., xN unchanged (this would

> suggest an exclusive variable tuple to me). I'll define a tuple, call it

> non_x1_x2_vars == <<x3, ..., xN>>, and then just write UNCHANGED

> non_x1_x2_vars in the aforementioned actions. As long as you write all

> your actions in one module, this seems to work really well. Not to

> mention when you have 10+ variables in a spec, it becomes next to

> impossible to visually inspect whether you have included all the

> unchanged variables.

>

> I first saw this little trick in the raft spec

> <https://github.com/ongardie/raft.tla/blob/master/raft.tla> where they

> use several (what I would call) inclusive variable tuples.

Hi,

have you tried *simulating* the specs with TLC for a few seconds to find

any missing variables in UNCHANGED statements? I haven't yet, but I

would expect the trick to catch most of them.

Markus

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**References**:**[tlaplus] How do you do functions of structures?***From:*Hillel Wayne

**Re: [tlaplus] How do you do functions of structures?***From:*Isaac DeFrain

**Re: [tlaplus] How do you do functions of structures?***From:*Markus Kuppe

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