old_contents: def topological_sort_recur():
  	"""Topological Sorting by Recursion."""
  	pass
  
  def topological_sort():
  	"""Topological Sorting for Directed Acyclic Graph (DAG)."""
  	pass
  
  
  def main():
  	# DAG.
  	adjacency_dict = {
  	    '0': {},
  	    '1': {},
  	    '2': {'3'},
  	    '3': {'1'},
  	    '4': {'0', '1'},
  	    '5': {'0', '2'}
  	}
  
  if __name__ == '__main__':
  	main()
  
new_contents: def topological_sort_recur(adjacency_dict, start_vertex,
  	                       visited_set, finish_ls):
  	"""Topological Sorting by Recursion."""
  	pass
  
  def topological_sort(adjacency_dict):
  	"""Topological Sorting for Directed Acyclic Graph (DAG)."""
  	pass
  
  
  def main():
  	# DAG.
  	adjacency_dict = {
  	    '0': {},
  	    '1': {},
  	    '2': {'3'},
  	    '3': {'1'},
  	    '4': {'0', '1'},
  	    '5': {'0', '2'}
  	}
  
  if __name__ == '__main__':
  	main()
  
subject: Add function arguments