def _find_instantiations(self, span, constituents):
        rv = []
        for production in self._grammar.productions():
            childlists = self._match_rhs(production.rhs(), span, constituents)

            for childlist in childlists:
                rv.append( (production, childlist) )
        return rv
:return: a list of the production instantiations that cover a
dataset/ETHPy150Open nltk/nltk/nltk/parse/viterbi.py/ViterbiParser._find_instantiations