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Understand the problem
Restate the problem precisely. Interviewers reward candidates who pause, define the contract, and name the guarantees before coding.
There is a new alien language that uses the English alphabet. However, the order of the letters is unknown to you. You are given a list of strings `words` from the alien language's dictionary. Now it is claimed that the strings in `words` are sorted lexicographically by the rules of this new language. If this claim is incorrect, and the given arrangement of strings in `words` cannot correspond to any order of letters, return `""`. Otherwise, return a string of the unique letters in the new alien language sorted in lexicographically increasing order by the new language's rules.
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