Craft a musical composition that adheres to the specified musical theme and letter-based structure.
X:1
L:1/4
M:6/4
K:D
['d) A d3 A2', 'F/G/ A3/2 B/ A F D F']  
X:1
L:1/4
M:6/4
K:D
 B/c/ | d2 (A B/c/ d) A | d3 A2 B | =c3/2 d/ c c G E | =c3 E2 B/c/ | d2 A (B/c/ d) A | d3 A2 G | 
 F D F E C E | D3- D2 :: F/G/ | A3/2 B/ A F D F | A3 E2 F | G3/2 A/ G E C E | G3 E2 F/G/ | 
 A3/2 B/ A F D F | A3 a2 g | (f/g/ a) f e d c | d3- d2 :|  