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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def is_chief(task: backend.Task, run_name: str):
 """Returns True if task is chief task in the corresponding run"""

  global run_task_dict
  if run_name not in run_task_dict:
    return True
  task_list = run_task_dict[run_name]
  assert task in task_list, f"Task {task.name} doesn't belong to run {run_name}"
  return task_list[0] == task