a-a aaa aaf aan aao aap af- afa aff afn afo afp an- ana anf ann ano anp aoa aof aon aoo aop ap- apa apf apn apo app faa faf fan fao fap ffa fff ffn ffo ffp fna fnf fnn fnp foa fof fon foo fop fpa fpn fpo fpp naa naf nan nao nap nfa nff nfn nfo nfp nna nnf nnn nno nnp no- noa nof non noo nop npa npf npn npo npp oaa oaf oan oao oap of- ofa off ofn ofo ofp on- ona onf onn ono onp oo- ooa oof oon ooo oop op- opa opf opn opo opp p-p paa paf pan pao pap pfa pff pfn pfo pfp pn- pna pnf pnn pno pnp poa pof pon poo pop ppa ppf ppn ppo ppp