Can you name a mathematical theorem that is simple to state and relatively simple to prove, was essential to your research or to a work you found interesting and significant, has the potential to be applied in a wide variety of fields, and is not part of the curriculum of what "every mathematician should know"?
closed as not constructive by José Figueroa-O'Farrill, Daniel Moskovich, Charles Siegel, Zev Chonoles, Bruce Westbury Apr 27 '11 at 15:27
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