def _is_inside(self, span1, span2, covered_spans):
        """Returns True if both `span1` and `span2` fall within
        `covered_spans`.

        :param span1: start and end indices of a span
        :type span1: 2-`tuple` of `int`
        :param span2: start and end indices of a span
        :type span2: 2-`tuple` of `int`
        :param covered_spans: lists of start and end indices for parts
                              of the texts already covered by a sequence
        :type covered_spans: `list` of two `list`s of 2-`tuple` of `int`
        :rtype: `bool`

        """
        if self._is_span_inside(span1, covered_spans[0]) and \
           self._is_span_inside(span2, covered_spans[1]):
            return True
        return False