a-a a-b a-i aaa aab aai aar aas ab- aba abb abi abr abs ai- aia aib aii air ais ar- ara arb ari arr ars as- asa asb asi asr ass baa bab bai bar bas bba bbb bbi bbr bbs bi- bia bib bii bir bis bra brb bri brr brs bsa bsb bsi bsr bss ia- iaa iab iai iar ias iba ibb ibi ibr ibs iia iib iii iir iis ir- ira irb iri irr irs is- isa isb isi isr iss ra- raa rab rai rar ras rba rbb rbi rbr rbs ria rib rii rir ris rra rrb rri rrr rrs rsa rsb rsi rsr rss saa sab sai sar sas sba sbb sbi sbr sbs sia sib sii sir sis sr- sra srb sri srr srs ss- ssa ssb ssi ssr sss