a-a a-b aaa aab aad aao aar ab- aba abb abd abo abr ad- ada adb add ado adr aoa aob aod aoo aor ar- ara arb ard aro arr baa bab bad bao bar bba bbb bbd bbo bbr bda bdb bdd bdo bdr boa bob bod boo bor bra brb brd bro brr daa dab dad dao dar dba dbb dbd dbo dbr dda ddb ddd ddo ddr doa dob dod doo dor dra drb drd dro drr oaa oab oad oao oar ob- oba obb obd obo obr oda odb odd odo odr oo- ooa oob ood ooo oor or- ora orb ord oro orr ra- raa rab rad rao rar rba rbb rbd rbo rbr rda rdb rdd rdo rdr roa rob rod roo ror rra rrb rrd rrr