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*From*: Andrew Helwer <andrew.helwer@xxxxxxxxx>*Date*: Thu, 22 Apr 2021 06:37:59 -0700 (PDT)*References*: <6841633b-0f09-4fa9-bedf-1d2345f680dbn@googlegroups.com>

Hi Huailin,

The formula x' + 1 = y + z is syntactically valid and can be used in an action property, but if you want to use TLC it cannot be used in an action itself. See Specifying Systems p238 for the expressions TLC can handle when computing successor states; they include expressions of the form:

- x' = e
- x' \in S
- UNCHANGED x

Andrew

On Wednesday, April 21, 2021 at 11:48:27 PM UTC-4 hua...@xxxxxxxxx wrote:

Folks,For an TLA's action, which is essentially a boolean _expression_, does it ONLY relate to two variables(primed or non-primed)?For instance, x' + 1 =y. (Please refer to Section 2.3 in Lamport's seminal paper "The Temporal Logic of Actions"-ACM 1993).Can we have an x' + 1 = y+z as an action? If yes, how we define the "old state" and the new state with the postfix notation? maybe define a super-state to cover (y, z)?Thanks huge,Huailin

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**Follow-Ups**:**Re: [tlaplus] Re: About Action***From:*Huailin

**References**:**[tlaplus] About Action***From:*hua...@xxxxxxxxx

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