During the ”snowball Earth” period about 700m years ago, Earth’s climate shut down. The planet was encased in ice and insulated from seasonal variations: spring, summer, autumn and winter all stopped. Or at least that was the theory.
There can be multiple possible certificates in the presence of duplicates. Our proof producing method only produces one of them (a lex minimal one kind of).
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李铃铛曾经是个晕船很严重的人，经常晕船呕吐，但她已经下定了决心，就算晕船也要学！
• （本文仅为作者个人观点，不代表本报立场）