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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 lemma(lemma_key):
 """Returns the Lemma object with the given key. Parameters lemma_key : str Key of the returned lemma. Returns ------- Lemma Lemma matching the `lemma_key`. """

    if lemma_key in LEMMAS_DICT:
        return LEMMAS_DICT[lemma_key]
    split_lemma_key = lemma_key.split('.')

    synset_key = '.'.join(split_lemma_key[:3])
    lemma_literal = split_lemma_key[3]

    lemma_obj = Lemma(synset_key,lemma_literal)
    LEMMAS_DICT[lemma_key] = lemma_obj
    return lemma_obj