a-a a-b a-c aaa aab aac aao aap ab- aba abb abc abo abp ac- aca acb acc aco acp aoa aob aoc aoo aop ap- apa apb apc apo app b-p baa bab bac bao bap bba bbb bbc bbo bbp bca bcb bcc bco bcp boa bob boc boo bop bpa bpb bpc bpo bpp c-- caa cab cac cao cap cba cbb cbc cbo cbp cca ccb ccc cco ccp co- coa cob coc coo cop cpa cpb cpc cpo cpp oaa oab oac oao oap ob- oba obb obc obo obp oc- oca ocb occ oco ocp oo- ooa oob ooc ooo oop op- opa opb opc opo opp p-p paa pab pac pao pap pba pbb pbc pbo pbp pca pcb pcc pco pcp poa pob poc poo pop ppa ppb ppc ppo ppp