type Set = {
    clear->Void
    isEmpty->Void
    add(_:T)->Void
    removeValue(_:T)->T
    contains(_:T)->Boolean
    containsAll(_:Set)->Boolean
    clone->Set
    addAll(_:Set)->Void
    retainAll(_:Set)->Void
    removeAll(_:Set)->Void
    iterator->Iterator
    size->Number
    asString->String}