Utilizing the provided musical theme and letter-based structure, compose a piece of music.
X:1
L:1/8
M:4/4
K:G
['B G<GB>G A=FFA G<GB>G AGBG D>GBG A=FFA', 'G3 B GGg_B A=FFA G<Ggd gagd =fgfc']  
X:1
L:1/8
M:4/4
K:G
 B | G<GB>G A=FFA | G<GB>G AGBG | D>GBG A=FFA | GcBA G3 :: B | GGg_B A=FFA | G<Ggd gagd | 
 =fgfc AFFA | (GcBA) G3 :|  