[tlaplus] Re: Type checking and custom infinite sets

[Leslie Lamport <tlaplus.ll@xxxxxxxxx>]

A predicate does not define a set.   The TLA+ operators for constructing sets are listed under the "Sets" heading on the "Constant Operators" section of:

   https://lamport.azurewebsites.net/tla/summary-standalone.pdf

If the "set" you want to define cannot be expressed with them, it is probably not what mathematicians define to be a set.

Leslie

On Friday, November 5, 2021 at 11:05:58 AM UTC-7 Chris Jensen wrote:

Hi!
When you have a type invariant for a system like Paxos, you can check that
for example ballot numbers are members of the set of natural numbers.

What I am trying to do (and can't seem to find any documentation on) is how
to define my own infinite sets (for example one which is defined by some
predicate).
This is specifically just for type checking, and thus should just be
checking whether a value is an element of a set, hence should just be able
to use the predicate.

Is there any way to do this?

--
Thanks,

Chris

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