有两句关键的话翻译掉了。

If it is impossible to solve the problem, print

Impossible. Otherwise, print the sought crossword.

All the empty squares should be marked as dots.

1 ： 不行输出"impossible"

If there can be several solutions to that

problem, print the lexicographically minimum

one. I.e. the solution where the first line is

less than the first line of other solutions

should be printed. If the two lines are equal,

compare the second lines and so on. The

lexicographical comparison of lines is realized

by the < operator in the modern programming

languages.

2 : 字典序最小