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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_etexts(feature_name, value):
 """Looks up all the texts that have meta-data matching some criterion. Arguments: feature_name (str):
 The meta-data on which to select the texts. value (str):
 The value of the meta-data on which to filter the texts. Returns: frozenset: The set of all the Project Gutenberg text identifiers that match the provided query. Raises: UnsupportedFeature: If there is no MetadataExtractor registered that can extract meta-data for the given feature name. """

    matching_etexts = MetadataExtractor.get(feature_name).get_etexts(value)
    return frozenset(matching_etexts)