Craft a musical composition that adheres to the specified musical theme and letter-based structure.
X:1
L:1/8
M:2/2
K:G
['B2 cA', '=f2 e2']  
X:1
L:1/8
M:2/2
K:G
 dc | B2 cA B2 cA | BdcA B2 AG | d2 e^c d2 e^c | dfe^c d=cBA | e2 fd edcB | Adde dcBA | 
 B2 cA B2 AG | FGAB cBcA | G2 ge fdcA | FGAB cAFG | AGGF G2 FG | AGGF G2 :| GF | G2 =f2 e2 f2 | 
 G2 =fg fdcA | G2 g2 f2 g2 | d2 ga gedc | A2 =f2 e2 fe | d^cde fefg | agfa gfde | fdcA BGAF | 
 G2 ge fdcA | FGAB cAFG | AGGF G2 FG | AGGF G2 :|  