-er a-a a-b aaa aab aae aan aao aar ab- aba abb abe abn abo abr aea aeb aee aen aeo aer an- ana anb ane ann ano anr aoa aob aoe aon aoo aor ar- ara arb are arn aro arr baa bab bae ban bao bar bba bbb bbe bbn bbo bbr be- bea beb bee ben beo ber bna bnb bne bnn bno bnr boa bob boe bon boo bor bra brb bre brn bro brr eaa eab eae ean eao ear eba ebb ebe ebn ebo ebr eea eeb eee een eeo eer en- ena enb ene enn eno enr eo- eoa eob eoe eon eoo eor era erb ere ern ero err naa nab nae nan nao nar nba nbb nbe nbn nbo nbr ne- nea neb nee nen neo ner nna nnb nne nnn nno no- noa nob noe non noo nor nra nrb nre nrn nro nrr oaa oab oae oan oao oar ob- oba obb obe obn obo obr oea oeb oee oen oeo oer on- ona onb one onn ono onr oo- ooa oob oon ooo oor or- ora orb ore orn oro orr ra- raa rab rae ran rao rar rba rbb rbe rbn rbo rbr re- rea reb ree ren reo rer rna rnb rnn rno rnr roa rob roe ron roo ror rra rrb rrn rrr