a-a a-b aaa aab aae aaf aas ab- aba abb abe abf abs aea aeb aee aef aes af- afa afb afe aff afs as- asa asb ase asf ass baa bab bae baf bas bba bbb bbe bbf bbs be- bea beb bee bef bes bfa bfb bfe bff bfs bsa bsb bse bsf bss eaa eab eae eaf eas eba ebb ebe ebf ebs eea eeb eee eef ees ef- efa efb efe eff efs es- esa esb ese esf ess faa fab fae faf fas fba fbb fbe fbf fbs fea feb fee fef fes ffa ffe fff ffs fsa fsb fse fsf fss saa sab sae saf sas sba sbb sbe sbf sbs se- sea seb see sef ses sfa sfb sfe sff sfs ss- ssa ssb sse ssf sss