Create a musical composition employing the given alphabetic structure and melodic theme.
X:1
L:1/8
M:4/4
K:G
['gb eg']  
X:1
L:1/8
M:4/4
K:G
|: G2 g2 ag/f/ g2 | dg Bg dg Bg | G2 g2 ag/f/ g2 | fa AB cB cA | G2 g2 ag/f/ g2 | dg Bg dg Bg | 
 G2 g2 ag/f/ g2 | fg/a/ AB cd ef | gb eg dg B2 | gb eg fg af | gb eg dg B2 | AB cd ed ef | 
 gb eg dg B2 | gb eg fg af | gb fa eg dg | ca Bg AB cA :|  