Acionar a chave em nota entre colchete

7a 7a 7s 6a 5a 5s 6a 
7s 7s 6a 6s 6a 7a 7s 7a 8s 
7a 7a 7s 6a 5a 5s 6a 6a 7a 7a 7s 6a 7s 6a
6a 7a 8s 8s 9a 8s 7a 6a 7s 7s 6a 7s 7a 6a
7a 8s 9s 9a 8s 7a 6a 7s 7s 6a 5a 5s [8a]
7a 7a 7s 6a 5a 5s 6a 
7s 7s 6a 6s 6a 7a 7s 7a 8s 
7a 7a 7s 6a 5a 5s 6a 6a 7a 7a 7s 6a 7s 6a