Compose a piece of music that follows both the given musical theme and the letter-based structure provided.
X:1
L:1/8
M:6/8
K:G
['BGG DGG BGB dcB', 'G3 BGG DGG BGB BAG AFF DFF']  
X:1
L:1/8
M:6/8
K:G
|: BGG DGG | BGB dcB | cAA EAA | cAc edc | BGG DGG | BGB dcB | cBc Adc | BGG G3 :: BGG DGG | 
 BGB BAG | AFF DFF | AFA AGF | EGG DGG | CGG B,GG | cBc Adc | BGG G3 :|  