问题
I have the following spec:
------------------------------ MODULE Group ------------------------------
CONSTANTS People
VARIABLES members
Init == members \subseteq People
Next == members' = members
Group == Init /\ [][Next]_members
=============================================================================
(I simplified this spec to the point where it's not doing anything useful.)
When I try to run it through TLC, I get the following error:
In evaluation, the identifier members is either undefined or not an operator.
The error points to the Init line.
When I change the Init line to:
Init == members \in People
it validates fine.
I want the former functionality because I mean for members to be a collection of People, not a single person.
According to section 16.1.6 of Leslie Lamport's Specifying Systems, "TLA+ provides the following operators on sets:" and lists both \in and \subseteq.
Why is TLA+ not letting me use \subseteq?
回答1:
While that is a valid TLA+ expression, TLC can only assign next-state values to a variable x by the statements x' = e or x' \in S. See section 14.2.6 for details. This holds for the initial assignment, too. In your case, you probably want members \in SUBSET People.
来源：https://stackoverflow.com/questions/53426052/in-works-while-subseteq-gives-a-identifier-undefined-error