a-a a-b a-i aaa aab aaf aai aar aas ab- aba abb abf abi abr abs af- afa afb aff afi afr afs ai- aia aib aif aii air ais ar- ara arb arf ari arr ars as- asa asb asf asi asr ass baa bab baf bai bar bas bba bbb bbf bbi bbr bbs bfa bfb bff bfi bfr bfs bi- bia bib bif bii bir bis bra brb brf bri brr brs bsa bsb bsf bsi bsr bss faa fab faf fai far fas fba fbb fbf fbi fbr fbs ffa fff ffi ffr ffs fia fib fif fii fir fis fra frb frf fri frr frs fsa fsb fsf fsi fsr fss i-f ia- iaa iab iaf iai iar ias iba ibb ibf ibi ibr ibs ifa ifb iff ifi ifr ifs iia iib iif iii iir iis ir- ira irb irf iri irr irs is- isa isb isf isi isr iss ra- raa rab raf rai rar ras rba rbb rbf rbi rbr rbs rfa rfb rff rfi rfr rfs ria rib rif rii rir ris rra rrb rrf rri rrr rrs rsa rsb rsf rsi rsr rss saa sab saf sai sar sas sba sbb sbf sbi sbr sbs sfa sfb sff sfi sfr sfs sia sib sif sii sir sis sr- sra srb srf sri srr srs ss- ssa ssb ssf ssi ssr sss