-er a-a a-b a-i aaa aab aae aag aai aar aax ab- aba abb abe abg abi abr abx aea aeb aee aeg aei aer aex ag- aga agb age agg agi agr agx ai- aia aib aie aig aii air aix ar- ara arb are arg ari arr arx ax- axa axe axi axr axx baa bab bae bag bai bar bax bba bbb bbe bbg bbi bbr bbx be- bea beb bee beg bei ber bex bga bgb bge bgg bgi bgr bgx bi- bia bib bie big bii bir bix bra brb bre brg bri brr brx bxb bxi bxx eaa eab eae eag eai ear eax eba ebb ebe ebg ebi ebr ebx eea eeb eee eeg eer eex ega egb ege egg egi egr egx eia eib eie eig eii eir eix era erb ere erg eri err ex- exa exe exi exr exx gaa gab gae gag gai gar gba gbe gbg gbi gbr gbx ge- gea geb gee geg gei ger gex gga ggb ggg ggi ggr gia gib gie gig gii gir gra grb gre grg gri grr grx gxa ia- iaa iab iae iag iai iar iba ibb ibe ibg ibi ibr ibx ie- iea iee ieg iei ier iex iga igb ige igg igi igr iia iib iie iii iir iix ir- ira irb ire irg iri irr irx ixe ixi ra- raa rab rae rag rai rar rax rba rbb rbe rbg rbi rbr rbx re- rea reb ree reg rei rer rex rga rgb rge rgg rgi rgr rgx ria rib rie rig rii rir rix rra rrb rrg rri rrr rxr xaa xag xar xbe xbr xbx xee xeg xer xex xge xgi xia xie xii xix xrx xxi xxx