a-a a-b aaa aab aao aap aas ab- aba abb abo abp abs aoa aob aoo aop aos ap- apa apb apo app aps as- asa asb aso asp ass b-p baa bab bao bap bas bba bbb bbo bbp bbs boa bob boo bop bos bpa bpb bpo bpp bps bsa bsb bso bsp bss oaa oab oao oap oas ob- oba obb obo obp obs oo- ooa oob ooo oop oos op- opa opb opo opp ops os- osa osb oso osp oss p-p paa pab pao pap pas pba pbb pbo pbp pbs poa pob poo pop pos ppa ppb ppo ppp pps ps- psa psb pso psp pss saa sab sao sap sas sba sbb sbo sbp sbs soa sob soo sop sos spa spb spo spp sps ss- ssa ssb sso ssp sss