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