a-a a-b aaa aab aaf aap aar ab- aba abb abf abp abr af- afa afb aff afp afr ap- apa apb apf app apr ar- ara arb arf arp arr b-p baa bab baf bap bar bba bbb bbf bbp bbr bfa bfb bff bfp bfr bpa bpb bpf bpp bpr bra brb brf brp brr faa fab faf fap far fba fbb fbf fbp fbr ffa fff ffp ffr fpa fpb fpp fpr fra frb frf frp frr p-p paa pab paf pap par pba pbb pbf pbp pbr pfa pfb pff pfp pfr ppa ppb ppf ppp ppr pra prb prf prp prr ra- raa rab raf rap rar rba rbb rbf rbp rbr rfa rfb rff rfp rfr rpa rpb rpf rpp rpr rra rrb rrf rrp rrr