Utilizing the provided musical theme and letter-based structure, compose a piece of music.
X:1
L:1/8
M:2/2
K:G
['B>G{A} (3GFG D>G{A}', 'dggf gagf dgga bgag']  
X:1
L:1/8
M:2/2
K:G
 B>G{A} (3GFG D>G{A} (3GFG | BGGB cedc | B>G{A} (3GFG D>G{A} GFG | AFFA =fdcA | 
 BG{A} GFG DG{A} GFG | BGGB cedc | BABc de=fd | cAFA =fdcA || dggf gagf | dgga bgag | de=fe fgfe | 
 d=feg fdcA | dggf gagf | dgga bgag | bgag bgag | d=feg fdcA ||  