code: def __repr__(self):
      chain_list = []
      for i in range(len(self)):
          chain_list.append(
              (
                  self.ftime[i],
                  self.btime[i],
                  self.x[i],
                  self.xbar[i],
                  self.ftmp[i],
                  self.btmp[i],
              )
          )
      i = len(self)
      chain_list.append(
          (
              None,
              self.btime[i],
              self.x[i],
              self.xbar[i],
              None,
              self.btmp[i],
          )
      )
      return chain_list.__repr__()
  
imports: import math
  from abc import ABC
  from typing import List
  from torch.utils._pytree import tree_map
label_desc: Use image node_id 3 for calling the Chain obj's underlying member method code with example usage: obj.__repr__() and returns: chain_list