a-a a-b aaa aab aao aap aas aax ab- aba abb abo abp abs abx aoa aob aoo aop aos aox ap- apa apb apo app aps apx as- asa asb aso asp ass asx ax- axa axo axp axs axx b-p baa bab bao bap bas bax bba bbb bbo bbp bbs bbx boa bob boo bop bos box bpa bpb bpo bpp bps bpx bsa bsb bso bsp bss bsx bxb bxo bxx oaa oab oao oap oas oax ob- oba obb obo obp obs obx oo- ooa oob ooo oop oos oox op- opa opb opo opp ops opx os- osa osb oso osp oss osx ox- oxa oxb oxo oxx p-p paa pab pao pap pas pax pba pbb pbo pbp pbs pbx poa pob poo pop pos pox ppa ppb ppo ppp pps ppx ps- psa psb pso psp pss psx pxs saa sab sao sap sas sax sba sbb sbo sbp sbs sbx soa sob soo sop sos sox spa spb spo spp sps spx ss- ssa ssb sso ssp sss ssx sxs xaa xap xas xbx xoa xoo xop xos xox xpa xpb xpo xpp xps xsa xsb xsp xss xxo xxp xxx