a-a a-c aaa aac aaf aar aas ac- aca acc acf acr acs af- afa afc aff afr afs ar- ara arc arf arr ars as- asa asc asf asr ass c-- caa cac caf car cas cca ccc ccf ccr ccs cfa cfc cff cfr cfs cra crc crf crr crs csa csc csf csr css faa fac faf far fas fca fcc fcf fcr fcs ffa ffc fff ffr ffs fra frc frf frr frs fsa fsc fsf fsr fss ra- raa rac raf rar ras rca rcc rcf rcr rcs rfa rfc rff rfr rfs rra rrc rrf rrr rrs rsa rsc rsf rsr rss saa sac saf sar sas sca scc scf scr scs sfa sfc sff sfr sfs sr- sra src srf srr srs ss- ssa ssc ssf ssr sss