-er a-a a-b aaa aab aae aan aar ab- aba abb abe abn abr aea aeb aee aen aer an- ana anb ane ann anr ar- ara arb are arn arr baa bab bae ban bar bba bbb bbe bbn bbr be- bea beb bee ben ber bna bnb bne bnn bnr bra brb bre brn brr eaa eab eae ean ear eba ebb ebe ebn ebr eea eeb eee een eer en- ena enb ene enn enr era erb ere ern err naa nab nae nan nar nba nbb nbe nbn nbr ne- nea neb nee nen ner nna nnb nne nnn nra nrb nre nrn nrr ra- raa rab rae ran rar rba rbb rbe rbn rbr re- rea reb ree ren rer rna rnb rnn rnr rra rrb rrn rrr