Macro vstd::assert_sets_equal

macro_rules! assert_sets_equal {
    [$($tail:tt)*] => { ... };
}

Prove two sets equal by extensionality. Usage is:

assert_sets_equal!(set1 == set2);

or,

assert_sets_equal!(set1 == set2, elem => {
    // prove that set1.contains(elem) iff set2.contains(elem)
});