'Determines whether or not the given ngram is in the thesaurus.
:param ngram: ngram to lookup
:type ngram: C{string}
:return: whether the given ngram is in the thesaurus.'

def __contains__(self, ngram):

    return reduce((lambda accum, fileid: (accum or (ngram in self._thesaurus[fileid]))), self._fileids, False)
