a-a a-c a-t aaa aac aas aat aax ac- aca acc acs act acx as- asa asc ass ast asx at- ata atc ats att atx ax- axa axs axt axx c-- caa cac cas cat cax cca ccc ccs cct ccx csa csc css cst csx cta ctc cts ctt ctx cxc cxs cxt cxx saa sac sas sat sax sca scc scs sct scx ss- ssa ssc sss sst ssx sta stc sts stt stx sxc sxs sxt t-x taa tac tas tat tax tca tcc tcs tct tcx tsa tsc tss tst tsx tta ttc tts ttt ttx txs txt xaa xac xas xat xcx xsa xsc xss xst xtc xts xtx xxx