a-a a-b a-i aaa aab aai aap aas ab- aba abb abi abp abs ai- aia aib aii aip ais ap- apa apb api app aps as- asa asb asi asp ass b-p baa bab bai bap bas bba bbb bbi bbp bbs bi- bia bib bii bip bis bpa bpb bpi bpp bps bsa bsb bsi bsp bss ia- iaa iab iai iap ias iba ibb ibi ibp ibs iia iib iii iip iis ipa ipb ipi ipp ips is- isa isb isi isp iss p-p paa pab pai pap pas pba pbb pbi pbp pbs pia pib pii pip pis ppa ppb ppi ppp pps ps- psa psb psi psp pss saa sab sai sap sas sba sbb sbi sbp sbs sia sib sii sip sis spa spb spi spp sps ss- ssa ssb ssi ssp sss