k1 = k1 k2 = k1r k3 = k2 k4 = k2r k5 = k3 k6 = k3r k7 = k4 k8 = k5 k9 = k5r k10 = k6 k11 = k6r k12 = k7 k13 = k7r k14 = k8 k15 = k9 k16 = k9r k17 = k10 k18 = k10r k19 = k11 k20 = env k21 = S k22 = U k23 = T