code: def update(self, action: torch.Tensor) -> 'ChecklistStatelet':
          
          checklist_addition = (self.terminal_actions == action).float()
          new_checklist = self.checklist + checklist_addition
          new_checklist_state = ChecklistStatelet(terminal_actions=self.terminal_actions,
                                                  checklist_target=self.checklist_target,
                                                  checklist_mask=self.checklist_mask,
                                                  checklist=new_checklist,
                                                  terminal_indices_dict=self.terminal_indices_dict)
          return new_checklist_state
docs: Takes an action index, updates checklist and returns an updated state.