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*From*: Leslie Lamport <tlaplus.ll@xxxxxxxxx>*Date*: Sat, 6 Nov 2021 04:27:02 -0700 (PDT)*Ironport-hdrordr*: A9a23:eHCQYqgiBnOREQeX/LChvjnFyHBQXlEji2hC6mlwRA09TyX4rbHToB1/73WYtN9/YgBFpTntAtjmfZqYz+8M3WH+VY3SKjUPlgOTXfZfBMjZsk7d8xSXzJ8o6U4YSdk2NDSSNykGsS5OizPIY+rIvuP3iZxA3t2uvkuFJDsCA8oQjTuRSDzraXGeIjM2e6bRO6Dy2iMtnUvbRZ14VLXcOpHFN9KzxOEjV6iJXffFPXIaALnkt0Lc1Fc3KXmlNud0aUIx/V7qywi19jDR1+GYqvm+jjXc22XQ45kTuNyk5MBEGNXksLlmFgnR*References*: <1636133961518.1536267474.2186325086.ref@aol.com> <1636133961518.1536267474.2186325086@aol.com>

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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**Follow-Ups**:**Re: [tlaplus] Re: Type checking and custom infinite sets***From:*'Chris Jensen' via tlaplus

**References**:**[tlaplus] Type checking and custom infinite sets***From:*'Chris Jensen' via tlaplus

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