Develop a musical piece using the given theme and incorporating the letter-based structure provided.
X:1
L:1/4
M:6/8
K:F
['f2 f f3/2', 'A2 B G2 G G3/2 A/ B']  
X:1
L:1/4
M:6/8
K:F
 c | f2 f f3/2 g/ a | f2 f f3/2 e/ d | c2 c A3/2 G/ F | A2 A A2 :: B | G2 G G3/2 A/ B | 
 c2 c c3/2 B/ A | (d e) c f2 d | (g a) f b2 g | (e c) f f2 e | f3- f2 |]  