a-a a-b aaa aab aad aae aaf ab- aba abb abd abe abf ad- ada adb add ade adf aea aeb aed aee aef af- afa afb afd afe aff baa bab bad bae baf bba bbb bbd bbe bbf bda bdb bdd bde bdf be- bea beb bed bee bef bfa bfb bfd bfe bff daa dab dad dae daf dba dbb dbd dbe dbf dda ddb ddd dde ddf de- dea deb ded dee def dfa dfb dfd dfe dff eaa eab ead eae eaf eba ebb ebd ebe ebf ed- eda edb edd ede edf eea eeb eed eee eef ef- efa efb efd efe eff faa fab fad fae faf fba fbb fbd fbe fbf fda fdb fdd fde fdf fea feb fed fee fef ffa ffd ffe fff