a-a a-b a-z aaa aab aao aap aaz ab- aba abb abo abp abz aoa aob aoo aop ap- apa apb apo app az- aza azb azo azp azz b-p baa bab bao bap baz bba bbb bbo bbp boa bob boo bop boz bpa bpb bpo bpp bza bzo bzp bzz oaa oab oao oap ob- oba obb obo obp oo- ooa oob ooo oop op- opa opb opo opp oza ozo ozz p-p paa pab pao pap paz pba pbb pbo pbp pbz poa pob poo pop poz ppa ppb ppo ppp ppz pzp zaa zab zao zap zaz zbb zo- zoa zob zoo zpo zpp zzz