Problems/Erdos-Szekeres Theorem

Erdos-Szekeres Theorem

CombinatoricsSOLVED
Year
1935
Difficulty
*****
Solved by
Paul Erdos & George Szekeres (1935)

Statement

Any sequence of more than (r-1)(s-1) distinct reals contains a monotone subsequence of length r or s.

n>(r−1)(s−1)  ⟹  ∃ monotone subsequence of length r or sn > (r-1)(s-1) \implies \exists\, \text{monotone subsequence of length } r \text{ or } s

About this Problem

Proved when Erdos was 22. The paper also posed the Happy Ending problem, named because it led to the marriage of Szekeres and Esther Klein.

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