a-a a-b aaa aab aao aap aar ab- aba abb abo abp abr aoa aob aoo aop aor ap- apa apb apo app apr ar- ara arb aro arp arr b-p baa bab bao bap bar bba bbb bbo bbp bbr boa bob boo bop bor bpa bpb bpo bpp bpr bra brb bro brp brr oaa oab oao oap oar ob- oba obb obo obp obr oo- ooa oob ooo oop oor op- opa opb opo opp opr or- ora orb oro orp orr p-p paa pab pao pap par pba pbb pbo pbp pbr poa pob poo pop por ppa ppb ppo ppp ppr pra prb pro prp prr ra- raa rab rao rap rar rba rbb rbo rbp rbr roa rob roo rop ror rpa rpb rpo rpp rpr rra rrb rrp rrr