code: def apply_raw_r_assimilation(last_syllable: str) -> str:
      
  
      if len(last_syllable) > 0:
          if last_syllable[-1] == "l":
              return last_syllable + "l"
          elif last_syllable[-1] == "s":
              return last_syllable + "s"
          elif last_syllable[-1] == "n":
              return last_syllable + "n"
      return last_syllable + "r"
docs: -r preceded by an -s-, -l- or -n- becomes respectively en -s, -l or -n.
  
      >>> apply_raw_r_assimilation("arm")
      'armr'
      >>> apply_raw_r_assimilation("ás")
      'áss'
      >>> apply_raw_r_assimilation("stól")
      'stóll'
      >>> apply_raw_r_assimilation("stein")
      'steinn'
      >>> apply_raw_r_assimilation("vin")
      'vinn'
  
  
      :param last_syllable: last syllable of an Old Norse word
      :return: