a-a a-b a-c aaa aab aac aan aao aar aax ab- aba abb abc abn abo abr abx ac- aca acb acc acn aco acr acx an- ana anb anc ann ano anr anx aoa aob aoc aon aoo aor aox ar- ara arb arc arn aro arr arx ax- axa axn axo axr axx baa bab bac ban bao bar bax bba bbb bbc bbn bbo bbr bbx bca bcb bcc bcn bco bcr bcx bna bnb bnc bnn bno bnr bnx boa bob boc bon boo bor box bra brb brn bro brr brx bxb bxn bxo bxx c-- caa cab cac can cao car cax cba cbb cbc cbn cbo cbr cbx cca ccb ccc ccn cco ccr ccx cn- cna cnb cnc cnn cno cnr cnx co- coa cob coc con coo cor cox cra crb crc crn cro crr crx cxc cxo cxr cxx naa nab nac nan nao nar nax nba nbb nbc nbn nbo nbr nbx nca ncb ncc ncn nco ncr ncx nna nnb nnc nnn nno no- noa nob noc non noo nor nox nra nrb nrc nrn nro nrr nrx nxc oaa oab oac oan oao oar oax ob- oba obb obc obn obo obr obx oc- oca ocb occ ocn oco ocr ocx on- ona onb onc onn ono onr onx oo- ooa oob ooc oon ooo oor oox or- ora orb orc orn oro orr orx ox- oxa oxb oxc oxn oxo oxx ra- raa rab rac ran rao rar rax rba rbb rbc rbn rbo rbr rbx rca rcb rcc rcn rco rcr rcx rna rnb rnc rnn rno rnr roa rob roc ron roo ror rox rra rrb rrc rrn rrr rxr xaa xac xan xar xbc xbr xbx xcb xcr xcx xna xnc xno xoa xoc xon xoo xor xox xrc xrx xxo xxx