Craft a musical composition that adheres to the specified musical theme and letter-based structure.
X:1
L:1/8
M:4/4
K:D
['FDEF D2', 'FDEF D2']  
X:1
L:1/8
M:4/4
K:D
 A,G,A,B, DEDB, | A,B,DF EDB,G, | A,CEF E2 EF | GEEG FDED | F A2 B A2 A=c | BAGB AFAg | 
 (3fgf ec dBAG |1 FDEF D2 DB, :|2 FDEF D2 dB || ABdc dedc | Acde fded | cdef edcd | edef gfeg | 
 (3fgf ec dBAd | BAFB ABde | fafe dBAG |1 FDEF D2 AB :|2 FDEF D2 DB, ||  