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# [tlaplus] Re: Variables with values unspecified but distinct from each other

If you put the definitions in my post in your spec and TLC reported the error you mentioned, then
you failed to pay attention to the words "when you create a model for it" in my post.

Leslie

On Monday, July 27, 2020 at 12:48:07 PM UTC-7, mmynsted wrote:
Thank you.
For some reason if I do not bind the CHOOSE like:

x == CHOOSE a \in S : a \notin {}

Then I get an error "TLC attempted to evaluate an unbounded CHOOSE"
So something like this is closer to what I am after.

F[n \in Nat] == 0 .. n
S(n) == F[n]
P(Q) == CHOOSE n \in S(Cardinality(Q) + 1) : n \notin Q

Red == P({})
Yellow == P({Red})
Green == P({Red, Yellow})
Foo == P({Red, Yellow, Green})

I will try to simplify that F, S, and P bits... It seems like I should be able to use LET, In to combine those into a single operator.

On Monday, July 27, 2020 at 1:00:34 PM UTC-5 Leslie Lamport wrote:
If your spec contains a definition of the form

x == CHOOSE b : b \notin S

then when you create a model for it, the Toolbox will add to the model the appropriate
incantation to substitute for x a model value named "x".  You could therefore write

x == CHOOSE a : a \notin {}
y == CHOOSE a : a \notin {x}
z == CHOOSE a : a \notin {x,y}

and you won't have to do any instantiation of constants.

Leslie

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