chor 1 2
chor 2 3
mu 1 2 3
chor 3 13
com 1 2 4
chor 4 13
mu 3 3 5   # abab
pwr 4 4 6
mu 5 6 7

pwr 3 3 8 # ababab
mu 7 8 9

mu 2 3 10
com 1 10 11
pwr 11 3 12
mu 9 12 13

iv 2 14
mu 1 14 15 # ab^-1
mu 8 15 16
mu 16 16 17
mu 17 5 18
mu 18 15 19
mu 19 15 20
chor 20 2
