'Implements Step 1a from "An algorithm for suffix stripping"
From the paper:
SSES -> SS                         caresses  ->  caress
IES  -> I                          ponies    ->  poni
ties      ->  ti
SS   -> SS                         caress    ->  caress
S    ->                            cats      ->  cat'

def _step1a(self, word):

    if (self.mode == self.NLTK_EXTENSIONS):
        if (word.endswith(u'ies') and (len(word) == 4)):
            return self._replace_suffix(word, u'ies', u'ie')
    return self._apply_rule_list(word, [(u'sses', u'ss', None), (u'ies', u'i', None), (u'ss', u'ss', None), (u's', u'', None)])
