Utilizing the provided musical theme and letter-based structure, compose a piece of music.
X:1
L:1/8
M:3/4
K:Bb
['c dBc', 'c def']  
X:1
L:1/8
M:3/4
K:Bb
 c | dBc AFc | dBc A2 c | dBc AFf | ecA B2 :: c | def AFc | def A2 c | def aFf | ecA B3 :|  