a-a a-b a-i aaa aab aaf aai aao aas ab- aba abb abf abi abo abs af- afa afb aff afi afo afs ai- aia aib aif aii aio ais aoa aob aof aoi aoo aos as- asa asb asf asi aso ass baa bab baf bai bao bas bba bbb bbf bbi bbo bbs bfa bfb bff bfi bfo bfs bi- bia bib bif bii bio bis boa bob bof boi boo bos bsa bsb bsf bsi bso bss faa fab faf fai fao fas fba fbb fbf fbi fbo fbs ffa fff ffi ffo ffs fia fib fif fii fis foa fob fof foi foo fos fsa fsb fsf fsi fso fss i-f ia- iaa iab iaf iai iao ias iba ibb ibf ibi ibo ibs ifa ifb iff ifi ifo ifs iia iib iif iii iio iis io- ioa iob iof ioi ioo ios is- isa isb isf isi iso iss o-i oaa oab oaf oai oao oas ob- oba obb obf obi obo obs of- ofa ofb off ofi ofo ofs oia oib oif oii oio ois oo- ooa oob oof ooi ooo oos os- osa osb osf osi oso oss saa sab saf sai sao sas sba sbb sbf sbi sbo sbs sfa sfb sff sfi sfo sfs sia sib sif sii sio sis soa sob sof soi soo sos ss- ssa ssb ssf ssi sso sss