Compose a piece of music using the specified alphabetical notation system and the provided theme.
X:1
L:1/4
M:4/4
K:G
['_B A G d2']  
X:1
L:1/4
M:4/4
K:G
 G | G _B A G | d2 d G | d d c _B | A2 z d | c _B A G | d2 _B G | A _B c A | G2 z |]  