Compose a piece of music that follows both the given musical theme and the letter-based structure provided.
X:1
L:1/8
M:2/2
K:D
['A3 G', 'f2 df']  
X:1
L:1/8
M:2/2
K:D
 A3 G FGAB | =c2 cG EFGE | A3 G FDFA | (3B^cd eg fdec | A3 G FGAB | =c2 cG EFGE | A3 G FDFA | 
 (3B^cd eg fdde |: f2 df afdf | e2 ^ce gece |1 f2 df afdB | ^ceag fdde :|2 faaf gfed | 
 (3B^cd eg fdec ||  