Compose a piece of music that follows both the given musical theme and the letter-based structure provided.
X:1
L:1/8
M:4/4
K:F
['Acc=B cAFG Acc=B c3 d', 'cA (3AAA fA (3AAA fAgA aA (3AAA']  
X:1
L:1/8
M:4/4
K:F
 FG | Acc=B cAFG | Acc=B c3 d | BddB dBFB | defd edcB | Acc=B cAFG | Acc=B c3 d | B3 c defd | 
 cAGA F2 :: AB | cA (3AAA fA (3AAA | fAgA aA (3AAA | BG (3GGG dG (3GGG | gGfG ecAB | 
 cA (3AAA fA (3AAA | fAgA aA (3AAA | Bcde fdcB | AFGE F2 :|  