-er a-a a-b a-c aaa aab aac aae aak aan aar ab- aba abb abc abe abk abn abr ac- aca acb acc ace ack acn acr aea aeb aec aee aek aen aer aka akb akc ake akk akn akr an- ana anb anc ane ank ann anr ar- ara arb arc are ark arn arr baa bab bac bae bak ban bar bba bbb bbc bbe bbk bbn bbr bca bcb bcc bce bck bcn bcr be- bea beb bec bee bek ben ber bka bkb bkc bke bkk bkn bkr bna bnb bnc bne bnk bnn bnr bra brb bre brk brn brr c-- caa cab cac cae cak can car cba cbb cbc cbe cbk cbn cbr cca ccb ccc cce cck ccn ccr ce- cea ceb cec cee cek cen cer cka ckb ckc cn- cna cnb cnc cne cnn cnr cra crb crc cre crk crn crr eaa eab eac eae eak ean ear eba ebb ebc ebe ebk ebn ebr ec- eca ecb ecc ece eck ecn ecr eea eeb eec eee eek een eer eka ekb ekc eke ekr en- ena enb enc ene enk enn enr era erb erc ere erk ern err ka- kaa kab kac kae kak kan kar kba kbb kbc kbe kbk kbn kbr kca kcb kcc kce kck kcn kcr ke- kea keb kec kee kek ken ker kkb kkc kke kkk kkn kkr kn- kna knc kne knk knn knr kra krc krk krn krr naa nab nac nae nak nan nar nba nbb nbc nbe nbk nbn nbr nca ncb ncc nce nck ncn ncr ne- nea neb nec nee nek nen ner nka nkc nke nkk nkn nkr nna nnb nnc nne nnk nnn nra nrb nrc nre nrk nrn nrr ra- raa rab rac rae rak ran rar rba rbb rbc rbe rbk rbn rbr rca rcb rcc rce rcn rcr re- rea reb rec ree rek ren rer rkb rkc rke rkk rna rnb rnc rnn rnr rra rrb rrc rrk rrn rrr