a-a a-b a-c aaa aab aac aak aap ab- aba abb abc abk abp ac- aca acb acc ack acp aka akb akc akk akp ap- apa apb apc apk app b-p baa bab bac bak bap bba bbb bbc bbk bbp bca bcb bcc bck bcp bka bkb bkc bkk bkp bpa bpb bpc bpp c-- caa cab cac cak cap cba cbb cbc cbk cbp cca ccb ccc cck ccp cka ckb ckc cpa cpb cpc cpk cpp ka- kaa kab kac kak kap kba kbb kbc kbk kbp kca kcb kcc kck kcp kkb kkc kkk kkp kpa kpc kpk kpp p-p paa pab pac pak pap pba pbb pbc pbk pbp pca pcb pcc pck pcp pka pkb pkc pkp ppa ppb ppc ppk ppp