def get_backward_span_repr(backward_encoder_out, span_start, span_end):
    """
    Get backward span representation
    """
    assert span_start <= span_end

    if span_end >= len(backward_encoder_out) - 1:
        backward_span_repr = backward_encoder_out[span_start]
    else:
        backward_span_repr = backward_encoder_out[span_start] - backward_encoder_out[span_end + 1]
    return backward_span_repr