radl : radl radl_sentence
                | radl_sentence

def p_radl(self, t):
        """radl : radl radl_sentence
                | radl_sentence"""

        if len(t) == 2:
            t[0] = RADL()
            t[0].add(t[1])
        else:
            t[0] = t[1]
            t[0].add(t[2])