a-a a-b aaa aab aae aak aas ab- aba abb abe abk abs aea aeb aee aek aes aka akb ake akk aks as- asa asb ase ask ass baa bab bae bak bas bba bbb bbe bbk bbs be- bea beb bee bek bes bka bkb bke bkk bks bsa bsb bse bsk bss eaa eab eae eak eas eba ebb ebe ebk ebs eea eeb eee eek ees eka ekb eke eks es- esa esb ese esk ess ka- kaa kab kae kak kas kba kbb kbe kbk kbs ke- kea keb kee kek kes kkb kke kkk kks ksa ksb kse ksk kss saa sab sae sak sas sba sbb sbe sbk sbs se- sea seb see sek ses sk- ska skb ske skk sks ss- ssa ssb sse ssk sss