'Validates a french catch phrase.
:param catch_phrase: The catch phrase to validate.'

@classmethod
def _is_catch_phrase_valid(cls, catch_phrase):

    for word in cls.words_which_should_not_appear_twice:
        begin_pos = catch_phrase.find(word)
        end_pos = catch_phrase.find(word, (begin_pos + 1))
        if ((begin_pos != (-1)) and (begin_pos != end_pos)):
            return False
    return True
