[tlaplus] Defining functions in TLAPS

[jack malkovick <sillymouse333@xxxxxxxxx>]

I'm experimenting again with TLPAS in order to learn stuff, and I guess this is the open/closed world problem.

I was trying to see if it's possible to define predicate P as TRUE only for value 1 and 2 and FALSE implicitly for any other value. Of course, none of the options below worked. 

Is the any way to do this?

THEOREM TestFunction ==
    ASSUME
        NEW S,
        NEW P \in [S -> BOOLEAN],
\*        \A s \in S : P[s] = IF s \in {1, 2} THEN TRUE ELSE FALSE
\*        P = (1 :> TRUE @@ 2 :> TRUE)
        P[1], P[2]
    PROVE
        P[3] => FALSE
    PROOF
        OBVIOUS

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