Utilizing the provided musical theme and letter-based structure, compose a piece of music.
X:1
L:1/8
M:4/4
K:D
['dfaf gfeg fdAG FGA=c BGFG EFGg', 'bagf g2']  
X:1
L:1/8
M:4/4
K:D
 A | dfaf gfeg | fdAG FGA=c | BGFG EFGg | fdec dcBA | dfaf gfeg | fdAG FGA=c | BGFG EFGg |1 
 fdec d3 :|2 fdec defg |: a2 af dfaf | dfaf bagf | g2 ge =cege | =cege agfg | a2 af dfaf | 
 dfaf bagf | g2 gf gbag |1 fdec defg :|2 fdec d3 |]  