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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 raise_double_modal_error(verb_phrase_doc):
 """A modal auxilary verb should not follow another modal auxilary verb"""

    prev_word = None
    for word in verb_phrase:
        if word.tag_ == 'MD' and prev_word.tag == 'MD':
            raise('DoubleModalError')
        prev_word = word