a-a a-b aaa aab aan aao aap ab- aba abb abn abo abp an- ana anb ann ano anp aoa aob aon aoo aop ap- apa apb apn apo app b-p baa bab ban bao bap bba bbb bbn bbo bbp bna bnb bnn bno bnp boa bob bon boo bop bpa bpb bpn bpo bpp naa nab nan nao nap nba nbb nbn nbo nbp nna nnb nnn nno nnp no- noa nob non noo nop npa npb npn npo npp oaa oab oan oao oap ob- oba obb obn obo obp on- ona onb onn ono onp oo- ooa oob oon ooo oop op- opa opb opn opo opp p-p paa pab pan pao pap pba pbb pbn pbo pbp pn- pna pnb pnn pno pnp poa pob pon poo pop ppa ppb ppn ppo ppp