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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def combine_types(types):
 # type: (Iterable[AbstractType]) -> AbstractType """Given some types, return a combined and simplified type. For example, if given 'int' and 'List[int]', return Union[int, List[int]]. If given 'int' and 'int', return just 'int'. """

    items = simplify_types(types)
    if len(items) == 1:
        return items[0]
    else:
        return UnionType(items)