a-a a-b aaa aab aae aan aao ab- aba abb abe abn abo aea aeb aee aen aeo an- ana anb ane ann ano aoa aob aoe aon aoo baa bab bae ban bao bba bbb bbe bbn bbo be- bea beb bee ben beo bna bnb bne bnn bno boa bob boe bon boo eaa eab eae ean eao eba ebb ebe ebn ebo eea eeb eee een eeo en- ena enb ene enn eno eo- eoa eob eoe eon eoo naa nab nae nan nao nba nbb nbe nbn nbo ne- nea neb nee nen neo nna nnb nne nnn nno no- noa nob noe non noo oaa oab oae oan oao ob- oba obb obe obn obo oea oeb oee oen oeo on- ona onb one onn ono oo- ooa oob oon ooo