Mortality Problem
For a given n, is the problem of determining if a set is mortal solvable? n=1 is solvable, n=2 is unknown, and n>=3 is unsolvable.
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MortalExplore with Wolfram|Alpha
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Cite this as:
Weisstein, Eric W. "Mortality Problem." From MathWorld--A Wolfram Resource. https://mathworld.wolfram.com/MortalityProblem.html