Names.CpredSourceThe *_env modules consider an order on user part of names the others consider an order on canonical part of names
The type of the elements in the set.
The type of sets.
add x s returns a set containing all elements of s, plus x. If x was already in s, then s is returned unchanged.
remove x s returns a set containing all elements of s, except x. If x was not in s, then s is returned unchanged.
equal s1 s2 tests whether the sets s1 and s2 are equal, that is, contain equal elements.