in function MI_score_turn

  lpx = - get_avg_nll(text + sep + m)
  response = text.split(sep)[-1]
  context = sep.join(text.split(sep)[1:-1])   # hree

the text starts with "<|endoftext|> " (without leading space)
the split function will return ["<|endoftext|> turn0...", "turn1", ...]
so the first turn will not be in the context