a-a a-b a-t aaa aab aao aar aat aax ab- aba abb abo abr abt abx aoa aob aoo aor aot aox ar- ara arb aro arr art arx at- ata atb ato atr att atx ax- axa axo axr axt axx baa bab bao bar bat bax bba bbb bbo bbr bbt bbx boa bob boo bor bot box bra brb bro brr brt brx bta btb bto btr btt btx bxb bxo bxx oaa oab oao oar oat oax ob- oba obb obo obr obt obx oo- ooa oob ooo oor oot oox or- ora orb oro orr ort orx ot- ota otb oto otr ott ox- oxa oxb oxo oxt oxx ra- raa rab rao rar rat rax rba rbb rbo rbr rbt rbx roa rob roo ror rot rox rra rrb rrr rrt rta rtb rto rtr rtt rtx rxr t-x taa tab tao tar tat tax tba tbb tbo tbr tbt to- toa tob too tor tot tox tra trb tro trr trt trx tta ttb tto ttr ttt ttx txt xaa xar xat xbr xbx xoa xoo xor xot xox xrt xrx xtr xtx xxo xxx