a-a a-b a-c a-z aaa aab aac aap aaz ab- aba abb abc abp abz ac- aca acb acc acp acz ap- apa apb apc app az- aza azb azp azz b-p baa bab bac bap baz bba bbb bbc bbp bca bcb bcc bcp bcz bpa bpb bpc bpp bza bzp bzz c-- caa cab cac cap caz cba cbb cbc cbp cbz cca ccb ccc ccp ccz cpa cpb cpc cpp cpz cz- czc p-p paa pab pac pap paz pba pbb pbc pbp pbz pca pcb pcc pcp ppa ppb ppc ppp ppz pzc pzp zaa zab zac zap zaz zbb zbc zpc zpp zzz