a-a a-b a-z aaa aab aao aar aaz ab- aba abb abo abr abz aoa aob aoo aor ar- ara arb aro arr arz az- aza azb azo azz baa bab bao bar baz bba bbb bbo bbr boa bob boo bor boz bra brb bro brr brz bza bzo bzr bzz oaa oab oao oar ob- oba obb obo obr oo- ooa oob ooo oor or- ora orb oro orr orz oza ozo ozz ra- raa rab rao rar raz rba rbb rbo rbr roa rob roo ror roz rra rrb rrr rza rzb rzo zaa zab zao zar zaz zbb zbr zo- zoa zob zoo zor zro zzr zzz