提示中 $\LaTeX$ 炸了，应为：

By definition, string $a=a_{1}a_{2}...\ a_{n}$ is lexicographically less than string $b=b_{1}b_{2}...\ b_{m}$ , if either $a$ is a prefix of $b$ and doesn't coincide with $b$ , or there exists such $i$ , that $a_{1}=b_{1},a_{2}=b_{2},...\ a_{i-1}=b_{i-1},a_{i}<b_{i}$ .

In the first sample half-palindrome substrings are the following strings — a, a, a, a, aa, aba, abaa, abba, abbabaa, b, b, b, b, baab, bab, bb, bbab, bbabaab (the list is given in the lexicographical order). By definition, string $a=a_{1}a_{2}...\ a_{n}$ is lexicographically less than string $b=b_{1}b_{2}...\ b_{m}$ , if either $a$ is a prefix of $b$ and doesn't coincide with $b$ , or there exists such $i$ , that $a_{1}=b_{1},a_{2}=b_{2},...\ a_{i-1}=b_{i-1},a_{i}<b_{i}$ .

In the first sample half-palindrome substrings are the following strings — a, a, a, a, aa, aba, abaa, abba, abbabaa, b, b, b, b, baab, bab, bb, bbab, bbabaab (the list is given in the lexicographical order).

By definition, string $ a=a_{1}a_{2}...\ a_{n} $ is lexicographically less than string $ b=b_{1}b_{2}...\ b_{m} $ , if either $ a $ is a prefix of $ b $ and doesn't coincide with $ b $ , or there exists such $ i $ , that $ a_{1}=b_{1},a_{2}=b_{2},...\ a_{i-1}=b_{i-1},a_{i}<b_{i} $ .

In the first sample half-palindrome substrings are the following strings — a, a, a, a, aa, aba, abaa, abba, abbabaa, b, b, b, b, baab, bab, bb, bbab, bbabaab (the list is given in the lexicographical order).