a-a a-b aaa aab aak aao aar aav ab- aba abb abk abo abr abv aka akb akk ako akr akv aoa aob aok aoo aor aov ar- ara arb ark aro arr arv av- ava avb avk avo avr baa bab bak bao bar bav bba bbb bbk bbo bbr bka bkb bkk bko bkr bkv boa bob bok boo bor bov bra brb brk bro brr brv bva bvb bvk bvo bvr bvv ka- kaa kab kak kao kar kav kba kbb kbk kbo kbr kkb kkk kkr kkv koa kob kok koo kor kra krk kro krr krv kva kvb kvk kvo kvr kvv oaa oab oak oao oar oav ob- oba obb obk obo obr obv oka okb okk oko okr oo- ooa oob ook ooo oor oov or- ora orb ork oro orr orv ov- ova ovb ovo ovv ra- raa rab rak rao rar rav rba rbb rbk rbo rbr rkb rkk rko rkv roa rob rok roo ror rov rra rrb rrk rrr rva rvb rvo rvr rvv v-a vaa vab vak vao var vav vba vbk vbo vbr vbv vka vkb voa vob vok voo vor vov vra vrb vrk vrr vva vvb vvo vvr vvv