a-a a-b a-c aaa aab aac aae aaf ab- aba abb abc abe abf ac- aca acb acc ace acf aea aeb aec aee aef af- afa afb afc afe aff baa bab bac bae baf bba bbb bbc bbe bbf bca bcb bcc bce bcf be- bea beb bec bee bef bfa bfb bfc bfe bff c-- caa cab cac cae caf cba cbb cbc cbe cbf cca ccb ccc cce ccf ce- cea ceb cec cee cef cfa cfb cfc cfe cff eaa eab eac eae eaf eba ebb ebc ebe ebf ec- eca ecb ecc ece ecf eea eeb eec eee eef ef- efa efb efc efe eff faa fab fac fae faf fba fbb fbc fbe fbf fca fcb fcc fce fcf fea feb fec fee fef ffa ffc ffe fff