code: def common_ancestor(c):
      
      span1 = _to_span(c[0])
      span2 = _to_span(c[1])
      ancestor1 = np.array(span1.sentence.xpath.split("/"))
      ancestor2 = np.array(span2.sentence.xpath.split("/"))
      min_len = min(ancestor1.size, ancestor2.size)
      return list(ancestor1[: np.argmin(ancestor1[:min_len] == ancestor2[:min_len])])
docs: Return the path to the root that is shared between a binary-Mention Candidate.
  
      In particular, this is the common path of HTML tags.
  
      :param c: The binary-Mention Candidate to evaluate
      :rtype: list of strings