Create a melodious piece that employs Bach's compositional methods.  
X:1
T:Music21 Fragment
T:Music21 Fragment
T:Music21
C:Music21
%%score 1 2 3 4
L:1/4
M:4/4
K:C
V:1 treble 
%%MIDI program 0
%%MIDI control 7 100
%%MIDI control 10 64
V:2 treble 
%%MIDI program 0
%%MIDI control 7 100
%%MIDI control 10 64
V:3 treble 
%%MIDI program 0
%%MIDI control 7 100
%%MIDI control 10 64
V:4 bass 
%%MIDI program 0
%%MIDI control 7 100
%%MIDI control 10 64
V:1
 z3 A | A F G A/G/ | F E !fermata!D A | A G c A/G/ | F G !fermata!A A/=B/ | c d/e/ f e | %6
 d ^c !fermata!d d | e d c B | A B !fermata!A d | c B c/_B/ A | A G !fermata!F A | _B A/G/ F G | %12
 F E !fermata!D z |] %13
V:2
 z3 F | E D D/E/ F/E/ | D ^C !fermata!A, F | F E/F/ G F/E/ | D/^C/ D/E/ !fermata!C F | E F/G/ A G | %6
 F/G/ A !fermata!A G | G ^G A A/G/ | A ^G !fermata!E =G | G F E F/E/ | D E !fermata!C D | %11
 G F/E/ D E/D/ | ^C/D/ D/C/ !fermata!A, z |] %13
V:3
 z3 D | A, A, D D/_B,/ | A, A,/G,/ !fermata!F, D | C C C C | D _B, !fermata!E, D | %5
 C _B, A, =B,/^C/ | D E !fermata!F =B, | =C D E F/E/ | E/D/ D/^C/ !fermata!C B, | =C D G, F, | %10
 F, C/_B,/ !fermata!A, D | D ^C D/=C/ _B, | A, A,/G,/ !fermata!^F, z |] %13
V:4
 z3"Dm" D, |"A/C#" ^C,"Dm" D,"Gm/Bb" _B,"Dm/F" F,/G,/ |"Dm/A" A,"A" A,,"Dm" !fermata!D,"Dm" D | %3
"F/A" A,/_B,/"C" C"C/E" E,"F" F, |"Bb" _B,"Gm/Bb" _B,,"A" !fermata!A,,"Dm" D, | %5
"Am" A,"Gm7" G,"F" F,"Em/G" G,/A,/ |"Bb" _B,"A" A,"Dm" !fermata!D,"G" G, | %7
"C" C"G#dim/B" B,"Am" A,"Bm7b5/D" D,/E,/ |"F" F,"E7" E,"A" !fermata!A,,"G" G,/F,/ | %9
"C/E" E,"Bdim/D" D,"C" C,"Dm" D,/C,/ |"Bbmaj7" _B,,"C" C,"F" !fermata!F,"D/F#" ^F, | %11
"Gm" G,"F+/A" A,"Bb" _B,/A,/"Edim/G" G, |"F+/A" A,"Asus4" A,,"D" !fermata!D, z |] %13  