[tlaplus] Checking if a set is a singleton

[Mathew Kuthur James <mathewkj2048@xxxxxxxxx>]

Hi,

In TLA+, given a set S, I understand that it's better to write S = {} than writing Cardinality(S) = 0. Is there a similar method to check if S is a singleton set, that beats using Cardinality(S) = 1? I am considering using singleton(S) == (\A x \in S : \A y \in S : x = y) /\ (S \= {})

In general, is the Cardinality function costly in terms of model-checking performance, such that there are performance gains by using set comprehension for checking if a set is a singleton or empty (readability concerns aside)? What sort of test would I need to run to observe the performance gap, if one exists?

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