-er a-a a-b a-c aaa aab aac aae aaf aak aan aar ab- aba abb abc abe abf abk abn abr ac- aca acb acc ace acf ack acn acr aea aeb aec aee aef aek aen aer af- afa afb afc afe aff afk afn afr aka akb akc ake akk akn akr an- ana anb anc ane anf ank ann anr ar- ara arb arc are arf ark arn arr baa bab bac bae baf bak ban bar bba bbb bbc bbe bbf bbk bbn bbr bca bcb bcc bce bcf bck bcn bcr be- bea beb bec bee bef bek ben ber bfa bfb bfc bfe bff bfn bfr bka bkb bkc bke bkf bkk bkn bkr bna bnb bnc bne bnf bnk bnn bnr bra brb bre brf brk brn brr c-- caa cab cac cae caf cak can car cba cbb cbc cbe cbf cbk cbn cbr cca ccb ccc cce ccf cck ccn ccr ce- cea ceb cec cee cef cek cen cer cfa cfb cfc cfe cff cfk cfn cfr cka ckb ckc cn- cna cnb cnc cne cnf cnn cnr cra crb crc cre crf crk crn crr eaa eab eac eae eaf eak ean ear eba ebb ebc ebe ebf ebk ebn ebr ec- eca ecb ecc ece ecf eck ecn ecr eea eeb eec eee eef eek een eer ef- efa efb efc efe eff efr eka ekb ekc eke ekf ekr en- ena enb enc ene enf enk enn enr era erb erc ere erf erk ern err faa fab fac fae faf fak fan far fba fbb fbc fbe fbf fbk fbn fbr fca fcb fcc fce fcf fck fcn fcr fea feb fec fee fef fek fen fer ffa ffc ffe fff ffk ffn ffr fka fkb fkc fkf fkk fna fnb fnc fne fnf fnk fnn fnr fra frb frc fre frf frk frn frr ka- kaa kab kac kae kaf kak kan kar kba kbb kbc kbe kbf kbk kbn kbr kca kcb kcc kce kck kcn kcr ke- kea keb kec kee kef kek ken ker kfa kfc kff kkb kkc kke kkk kkn kkr kn- kna knc kne knf knk knn knr kra krc krf krk krn krr naa nab nac nae naf nak nan nar nba nbb nbc nbe nbf nbk nbn nbr nca ncb ncc nce ncf nck ncn ncr ne- nea neb nec nee nef nek nen ner nfa nfb nfc nfe nff nfk nfn nfr nka nkc nke nkf nkk nkn nkr nna nnb nnc nne nnf nnk nnn nra nrb nrc nre nrf nrk nrn nrr ra- raa rab rac rae raf rak ran rar rba rbb rbc rbe rbf rbk rbn rbr rca rcb rcc rce rcf rcn rcr re- rea reb rec ree ref rek ren rer rfa rfb rfc rfe rff rfk rfn rfr rkb rkc rke rkf rkk rna rnb rnc rnn rnr rra rrb rrc rrf rrk rrn rrr