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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 get_stoplists():
 """Returns a collection of built-in stop-lists."""

    path_to_stoplists = os.path.dirname(sys.modules["justext"].__file__)
    path_to_stoplists = os.path.join(path_to_stoplists, "stoplists")

    stoplist_names = []
    for filename in os.listdir(path_to_stoplists):
        name, extension = os.path.splitext(filename)
        if extension == ".txt":
            stoplist_names.append(name)

    return frozenset(stoplist_names)