Develop a musical piece using the given theme and incorporating the letter-based structure provided.
X:1
L:1/8
M:4/4
K:Gmin
['G3 A (BA)(Bc) (dc)(df) g3', 'd3 g', 'fdB c2 d BGG G2', 'd2 g']  
X:1
L:1/8
M:4/4
K:Gmin
 D2 | G3 A (BA)(Bc) | (dc)(df) g3 a | b3 g (bg)(fe) | fdTcB c2 (B/c/d) | G3 A (BA)(Bc) | 
 (dc)(df) g3 b | (fd)(cB) (ce)(dc) |{c} B2 (AG) G2 :: (ga) | (ba)(gf) d3 g | (fd)(cd) B3 c | 
 d3 g T^f2 ga |{ga} b2 (ag) g3 a | (ba)(gf) (dc)(dg) | (fd)TcB Tc2 (Bc) | d3 g (fd)(cd) | 
{c} B2 (AG) G2 :|[M:6/8]"^Brisk" d | BGG G2 A | Bdg g2 a | b2 g fdB | fdB c2 d | BGG G2 A | 
 Bdg gbg | fdB c2 d | BGG G2 :: g/a/ | bgf dbg | fdB TcBc | d2 g ^fga | bab g2 a | b2 g fdg | 
 fdB cBc | d2 g fdc | BGG G2 :|  