docs: def get_amr_line(input_f):
          """
          Read the file containing AMRs. AMRs are separated by a blank line.
          Each call of get_amr_line() returns the next available AMR (in one-line form).
          Note: this function does not verify if the AMR is valid
  
          """
          cur_amr = []
          has_content = False
          for line in input_f:
              line = line.strip()
              if line == "":
                  if not has_content:
                      # empty lines before current AMR
                      continue
                  else:
                      # end of current AMR
                      break
              if line.strip().startswith("#"):
                  # ignore the comment line (starting with "#") in the AMR file
                  continue
              else:
                  has_content = True
                  cur_amr.append(line.strip())
          return "".join(cur_amr)