Develop a musical piece using the given theme and incorporating the letter-based structure provided.
X:1
L:1/8
Q:1/8=128
M:4/4
K:Amin
['A>G A<c B2']  
X:1
L:1/8
Q:1/8=128
M:4/4
K:Amin
|: G | E<A A>G A<c B2 | c<A A>G E<D D>E | A2 A>G A<c B2 | A<c B>d c3 G | E<A A>G A<c B2 | 
 c<A A>G E<D D>E | A2 A>G A<c B2 | A<c B>d c3 d | e<c a>e f<d d>f | e<c c>e d<B B>e | 
 e<c a>e f<d d>f | e<c d>e c<A A>e | e<c a>e f<d d>f | e<c d<B c<A G>B | A<c B>d c>e f>a | 
 g<e d>e c<A A :|  