def remove_redundant_items(items):
    # type: (List[AbstractType]) -> List[AbstractType]
    """Filter out redundant union items."""
    result = []
    for item in items:
        for other in items:
            if item is not other and is_redundant_union_item(item, other):
                break
        else:
            result.append(item)
    return result
Filter out redundant union items.