Generate a piece of music.  
X:1
T:Music21 Fragment
C:Music21
L:1/4
M:none
I:linebreak $
K:none
V:1 treble 
V:1
 z z z z | z z z z | z z z z | z z z G ||{/G} E F E C | B,2 B, G, | G, G, B, B, | C C2 G || %8
{/G} E F E C | B,2 B, G, | G, B, C D | B, C3 || %12  