Exception in Tkinter callback
Traceback (most recent call last):
  File "/usr/lib/python3.7/tkinter/__init__.py", line 1705, in __call__
    return self.func(*args)
  File "ajuda_redes.py", line 21, in ajuda_redes
    ajuda.add_command(label='URLs', command=mostrar_urls)
NameError: name 'mostrar_urls' is not defined